diff --git a/common/fake_hardware.h b/common/fake_hardware.h
index 2a8e81d..30c0897 100644
--- a/common/fake_hardware.h
+++ b/common/fake_hardware.h
@@ -19,10 +19,12 @@
 
 #include <map>
 #include <string>
+#include <utility>
 
 #include <base/time/time.h>
 
 #include "update_engine/common/hardware_interface.h"
+#include "update_engine/common/utils.h"
 
 namespace chromeos_update_engine {
 
@@ -207,6 +209,18 @@
   bool GetIsRollbackPowerwashScheduled() const {
     return powerwash_scheduled_ && save_rollback_data_;
   }
+  std::string GetVersionForLogging(
+      const std::string& partition_name) const override {
+    return partition_timestamps_[partition_name];
+  }
+  void SetVersion(const std::string& partition_name, std::string timestamp) {
+    partition_timestamps_[partition_name] = std::move(timestamp);
+  }
+  bool IsPartitionUpdateValid(const std::string& partition_name,
+                              const std::string& new_version) const override {
+    const auto old_version = GetVersionForLogging(partition_name);
+    return utils::IsTimestampNewer(old_version, new_version);
+  }
 
  private:
   bool is_official_build_{true};
@@ -230,6 +244,7 @@
   int64_t build_timestamp_{0};
   bool first_active_omaha_ping_sent_{false};
   bool warm_reset_{false};
+  mutable std::map<std::string, std::string> partition_timestamps_;
 
   DISALLOW_COPY_AND_ASSIGN(FakeHardware);
 };
diff --git a/common/hardware_interface.h b/common/hardware_interface.h
index 4f0305f..0fffbfb 100644
--- a/common/hardware_interface.h
+++ b/common/hardware_interface.h
@@ -142,6 +142,19 @@
   // If |warm_reset| is true, sets the warm reset to indicate a warm reset is
   // needed on the next reboot. Otherwise, clears the flag.
   virtual void SetWarmReset(bool warm_reset) = 0;
+
+  // Return the version/timestamp for partition `partition_name`.
+  // Don't make any assumption about the formatting of returned string.
+  // Only used for logging/debugging purposes.
+  virtual std::string GetVersionForLogging(
+      const std::string& partition_name) const = 0;
+
+  // Return true if and only if `new_version` is "newer" than the
+  // version number of partition `partition_name`. The notion of
+  // "newer" is defined by this function. Caller should not make
+  // any assumption about the underlying logic.
+  virtual bool IsPartitionUpdateValid(const std::string& partition_name,
+                                      const std::string& new_version) const = 0;
 };
 
 }  // namespace chromeos_update_engine
diff --git a/common/utils.cc b/common/utils.cc
index 3e3d830..bbb155f 100644
--- a/common/utils.cc
+++ b/common/utils.cc
@@ -820,7 +820,7 @@
   return base_code;
 }
 
-string StringVectorToString(const vector<string> &vec_str) {
+string StringVectorToString(const vector<string>& vec_str) {
   string str = "[";
   for (vector<string>::const_iterator i = vec_str.begin(); i != vec_str.end();
        ++i) {
@@ -849,7 +849,7 @@
                             encoded_hash.c_str());
 }
 
-bool ConvertToOmahaInstallDate(Time time, int *out_num_days) {
+bool ConvertToOmahaInstallDate(Time time, int* out_num_days) {
   time_t unix_time = time.ToTimeT();
   // Output of: date +"%s" --date="Jan 1, 2007 0:00 PST".
   const time_t kOmahaEpoch = 1167638400;
@@ -982,6 +982,29 @@
   return base::NumberToString(base::StringPieceHash()(str_to_convert));
 }
 
+static bool ParseTimestamp(const std::string& str, int64_t* out) {
+  if (!base::StringToInt64(str, out)) {
+    LOG(WARNING) << "Invalid timestamp: " << str;
+    return false;
+  }
+  return true;
+}
+
+bool IsTimestampNewer(const std::string& old_version,
+                      const std::string& new_version) {
+  if (old_version.empty() || new_version.empty()) {
+    LOG(WARNING)
+        << "One of old/new timestamp is empty, permit update anyway. Old: "
+        << old_version << " New: " << new_version;
+    return true;
+  }
+  int64_t old_ver = 0;
+  TEST_AND_RETURN_FALSE(ParseTimestamp(old_version, &old_ver));
+  int64_t new_ver = 0;
+  TEST_AND_RETURN_FALSE(ParseTimestamp(new_version, &new_ver));
+  return old_ver <= new_ver;
+}
+
 }  // namespace utils
 
 }  // namespace chromeos_update_engine
diff --git a/common/utils.h b/common/utils.h
index 23ac03d..5dfee3b 100644
--- a/common/utils.h
+++ b/common/utils.h
@@ -323,6 +323,12 @@
 // with |Excluder| as the exclusion name.
 std::string GetExclusionName(const std::string& str_to_convert);
 
+// Parse `old_version` and `new_version` as integer timestamps and
+// return true if `new_version` is larger/newer.
+// Returns true if either one is empty. Return false if
+bool IsTimestampNewer(const std::string& old_version,
+                      const std::string& new_version);
+
 }  // namespace utils
 
 // Utility class to close a file descriptor
diff --git a/common/utils_unittest.cc b/common/utils_unittest.cc
index ebcc548..37871d2 100644
--- a/common/utils_unittest.cc
+++ b/common/utils_unittest.cc
@@ -481,4 +481,12 @@
   IGNORE_EINTR(close(fd));
 }
 
+TEST(UtilsTest, ValidatePerPartitionTimestamp) {
+  ASSERT_FALSE(utils::IsTimestampNewer("10", "5"));
+  ASSERT_TRUE(utils::IsTimestampNewer("10", "11"));
+  ASSERT_FALSE(utils::IsTimestampNewer("10", "lol"));
+  ASSERT_FALSE(utils::IsTimestampNewer("lol", "ZZZ"));
+  ASSERT_TRUE(utils::IsTimestampNewer("10", ""));
+}
+
 }  // namespace chromeos_update_engine
diff --git a/hardware_android.cc b/hardware_android.cc
index 0bf05e4..659e67e 100644
--- a/hardware_android.cc
+++ b/hardware_android.cc
@@ -19,13 +19,17 @@
 #include <sys/types.h>
 
 #include <memory>
+#include <string>
+#include <string_view>
 
+#include <android-base/parseint.h>
 #include <android-base/properties.h>
 #include <base/files/file_util.h>
 #include <bootloader_message/bootloader_message.h>
 
 #include "update_engine/common/hardware.h"
 #include "update_engine/common/platform_constants.h"
+#include "update_engine/common/utils.h"
 
 using android::base::GetBoolProperty;
 using android::base::GetIntProperty;
@@ -223,4 +227,24 @@
   }
 }
 
+std::string HardwareAndroid::GetVersionForLogging(
+    const std::string& partition_name) const {
+  return android::base::GetProperty("ro." + partition_name + ".build.date.utc",
+                                    "");
+}
+
+bool HardwareAndroid::IsPartitionUpdateValid(
+    const std::string& partition_name, const std::string& new_version) const {
+  const auto old_version = GetVersionForLogging(partition_name);
+  // TODO(zhangkelvin)  for some partitions, missing a current timestamp should
+  // be an error, e.g. system, vendor, product etc.
+  auto applicable = utils::IsTimestampNewer(old_version, new_version);
+  if (!applicable) {
+    LOG(ERROR) << "Timestamp on partition " << partition_name
+               << " is newer than update. Partition timestamp: " << old_version
+               << " Update timestamp: " << new_version;
+  }
+  return applicable;
+}
+
 }  // namespace chromeos_update_engine
diff --git a/hardware_android.h b/hardware_android.h
index e0368f9..2e55f97 100644
--- a/hardware_android.h
+++ b/hardware_android.h
@@ -18,6 +18,7 @@
 #define UPDATE_ENGINE_HARDWARE_ANDROID_H_
 
 #include <string>
+#include <string_view>
 
 #include <base/macros.h>
 #include <base/time/time.h>
@@ -28,7 +29,7 @@
 namespace chromeos_update_engine {
 
 // Implements the real interface with the hardware in the Android platform.
-class HardwareAndroid final : public HardwareInterface {
+class HardwareAndroid : public HardwareInterface {
  public:
   HardwareAndroid() = default;
   ~HardwareAndroid() override = default;
@@ -58,6 +59,11 @@
   bool GetFirstActiveOmahaPingSent() const override;
   bool SetFirstActiveOmahaPingSent() override;
   void SetWarmReset(bool warm_reset) override;
+  [[nodiscard]] std::string GetVersionForLogging(
+      const std::string& partition_name) const override;
+  [[nodiscard]] bool IsPartitionUpdateValid(
+      const std::string& partition_name,
+      const std::string& new_version) const override;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(HardwareAndroid);
diff --git a/hardware_chromeos.cc b/hardware_chromeos.cc
index 2a83830..58f30db 100644
--- a/hardware_chromeos.cc
+++ b/hardware_chromeos.cc
@@ -384,4 +384,15 @@
 
 void HardwareChromeOS::SetWarmReset(bool warm_reset) {}
 
+std::string HardwareChromeOS::GetVersionForLogging(
+    const std::string& partition_name) const {
+  // TODO(zhangkelvin) Implement per-partition timestamp for Chrome OS.
+  return "";
+}
+bool HardwareChromeOS::IsPartitionUpdateValid(
+    const std::string& partition_name, const std::string& new_version) const {
+  // TODO(zhangkelvin) Implement per-partition timestamp for Chrome OS.
+  return true;
+}
+
 }  // namespace chromeos_update_engine
diff --git a/hardware_chromeos.h b/hardware_chromeos.h
index e14ae9a..49fed88 100644
--- a/hardware_chromeos.h
+++ b/hardware_chromeos.h
@@ -63,6 +63,10 @@
   bool GetFirstActiveOmahaPingSent() const override;
   bool SetFirstActiveOmahaPingSent() override;
   void SetWarmReset(bool warm_reset) override;
+  std::string GetVersionForLogging(
+      const std::string& partition_name) const override;
+  bool IsPartitionUpdateValid(const std::string& partition_name,
+                              const std::string& new_version) const override;
 
  private:
   friend class HardwareChromeOSTest;
diff --git a/payload_consumer/delta_performer.cc b/payload_consumer/delta_performer.cc
index 19d1297..aa0b4f5 100644
--- a/payload_consumer/delta_performer.cc
+++ b/payload_consumer/delta_performer.cc
@@ -1628,17 +1628,15 @@
     LOG(ERROR) << "Manifest contains deprecated fields.";
     return ErrorCode::kPayloadMismatchedType;
   }
-
-  if (manifest_.max_timestamp() < hardware_->GetBuildTimestamp()) {
-    LOG(ERROR) << "The current OS build timestamp ("
-               << hardware_->GetBuildTimestamp()
-               << ") is newer than the maximum timestamp in the manifest ("
-               << manifest_.max_timestamp() << ")";
+  TimestampCheckResult result = CheckTimestampError();
+  if (result == TimestampCheckResult::DOWNGRADE) {
     if (!hardware_->AllowDowngrade()) {
       return ErrorCode::kPayloadTimestampError;
     }
     LOG(INFO) << "The current OS build allows downgrade, continuing to apply"
                  " the payload with an older timestamp.";
+  } else if (result == TimestampCheckResult::FAILURE) {
+    return ErrorCode::kPayloadTimestampError;
   }
 
   // TODO(crbug.com/37661) we should be adding more and more manifest checks,
@@ -1647,6 +1645,53 @@
   return ErrorCode::kSuccess;
 }
 
+TimestampCheckResult DeltaPerformer::CheckTimestampError() const {
+  bool is_partial_update =
+      manifest_.has_partial_update() && manifest_.partial_update();
+  const auto& partitions = manifest_.partitions();
+  auto&& timestamp_valid = [this](const PartitionUpdate& partition) {
+    return hardware_->IsPartitionUpdateValid(partition.partition_name(),
+                                             partition.version());
+  };
+  if (is_partial_update) {
+    // for partial updates, all partition MUST have valid timestamps
+    // But max_timestamp can be empty
+    for (const auto& partition : partitions) {
+      if (!partition.has_version()) {
+        LOG(ERROR)
+            << "PartitionUpdate " << partition.partition_name()
+            << " does ot have a version field. Not allowed in partial updates.";
+        return TimestampCheckResult::FAILURE;
+      }
+      if (!timestamp_valid(partition)) {
+        // Warning because the system might allow downgrade.
+        LOG(WARNING) << "PartitionUpdate " << partition.partition_name()
+                     << " has an older version than partition on device.";
+        return TimestampCheckResult::DOWNGRADE;
+      }
+    }
+
+    return TimestampCheckResult::SUCCESS;
+  }
+  if (manifest_.max_timestamp() < hardware_->GetBuildTimestamp()) {
+    LOG(ERROR) << "The current OS build timestamp ("
+               << hardware_->GetBuildTimestamp()
+               << ") is newer than the maximum timestamp in the manifest ("
+               << manifest_.max_timestamp() << ")";
+    return TimestampCheckResult::DOWNGRADE;
+  }
+  // Otherwise... partitions can have empty timestamps.
+  for (const auto& partition : partitions) {
+    if (partition.has_version() && !timestamp_valid(partition)) {
+      // Warning because the system might allow downgrade.
+      LOG(WARNING) << "PartitionUpdate " << partition.partition_name()
+                   << " has an older version than partition on device.";
+      return TimestampCheckResult::DOWNGRADE;
+    }
+  }
+  return TimestampCheckResult::SUCCESS;
+}
+
 ErrorCode DeltaPerformer::ValidateOperationHash(
     const InstallOperation& operation) {
   if (!operation.data_sha256_hash().size()) {
diff --git a/payload_consumer/delta_performer.h b/payload_consumer/delta_performer.h
index 2d1768d..0718ef6 100644
--- a/payload_consumer/delta_performer.h
+++ b/payload_consumer/delta_performer.h
@@ -49,6 +49,12 @@
 // This class performs the actions in a delta update synchronously. The delta
 // update itself should be passed in in chunks as it is received.
 
+enum class TimestampCheckResult {
+  SUCCESS,
+  FAILURE,
+  DOWNGRADE,
+};
+
 class DeltaPerformer : public FileWriter {
  public:
   // Defines the granularity of progress logging in terms of how many "completed
@@ -310,6 +316,10 @@
   // Also see comment for the static PreparePartitionsForUpdate().
   bool PreparePartitionsForUpdate(uint64_t* required_size);
 
+  // Check if current manifest contains timestamp errors. (ill-formed or
+  // downgrade)
+  TimestampCheckResult CheckTimestampError() const;
+
   // Update Engine preference store.
   PrefsInterface* prefs_;
 
diff --git a/payload_consumer/delta_performer_integration_test.cc b/payload_consumer/delta_performer_integration_test.cc
index acbecad..c257b28 100644
--- a/payload_consumer/delta_performer_integration_test.cc
+++ b/payload_consumer/delta_performer_integration_test.cc
@@ -36,9 +36,12 @@
 #include "update_engine/common/constants.h"
 #include "update_engine/common/fake_boot_control.h"
 #include "update_engine/common/fake_hardware.h"
+#include "update_engine/common/fake_prefs.h"
 #include "update_engine/common/mock_prefs.h"
 #include "update_engine/common/test_utils.h"
 #include "update_engine/common/utils.h"
+#include "update_engine/hardware_android.h"
+#include "update_engine/payload_consumer/install_plan.h"
 #include "update_engine/payload_consumer/mock_download_action.h"
 #include "update_engine/payload_consumer/payload_constants.h"
 #include "update_engine/payload_consumer/payload_metadata.h"
@@ -125,7 +128,41 @@
 
 }  // namespace
 
-class DeltaPerformerIntegrationTest : public ::testing::Test {};
+class DeltaPerformerIntegrationTest : public ::testing::Test {
+ public:
+  void RunManifestValidation(const DeltaArchiveManifest& manifest,
+                             uint64_t major_version,
+                             ErrorCode expected) {
+    FakePrefs prefs;
+    InstallPlan::Payload payload;
+    InstallPlan install_plan;
+    DeltaPerformer performer{&prefs,
+                             nullptr,
+                             &fake_hardware_,
+                             nullptr,
+                             &install_plan,
+                             &payload,
+                             false /* interactive*/};
+    // Delta performer will treat manifest as kDelta payload
+    // if it's a partial update.
+    payload.type = manifest.partial_update() ? InstallPayloadType::kDelta
+                                             : InstallPayloadType::kFull;
+
+    // The Manifest we are validating.
+    performer.manifest_.CopyFrom(manifest);
+    performer.major_payload_version_ = major_version;
+
+    EXPECT_EQ(expected, performer.ValidateManifest());
+  }
+  void AddPartition(DeltaArchiveManifest* manifest,
+                    std::string name,
+                    int timestamp) {
+    auto& partition = *manifest->add_partitions();
+    partition.set_version(std::to_string(timestamp));
+    partition.set_partition_name(name);
+  }
+  FakeHardware fake_hardware_;
+};
 
 static void CompareFilesByBlock(const string& a_file,
                                 const string& b_file,
@@ -995,13 +1032,13 @@
   delete performer;
 }
 
-TEST(DeltaPerformerIntegrationTest, RunAsRootSmallImageTest) {
+TEST_F(DeltaPerformerIntegrationTest, RunAsRootSmallImageTest) {
   DoSmallImageTest(
       false, false, -1, kSignatureGenerator, false, kSourceMinorPayloadVersion);
 }
 
-TEST(DeltaPerformerIntegrationTest,
-     RunAsRootSmallImageSignaturePlaceholderTest) {
+TEST_F(DeltaPerformerIntegrationTest,
+       RunAsRootSmallImageSignaturePlaceholderTest) {
   DoSmallImageTest(false,
                    false,
                    -1,
@@ -1010,8 +1047,8 @@
                    kSourceMinorPayloadVersion);
 }
 
-TEST(DeltaPerformerIntegrationTest,
-     RunAsRootSmallImageSignaturePlaceholderMismatchTest) {
+TEST_F(DeltaPerformerIntegrationTest,
+       RunAsRootSmallImageSignaturePlaceholderMismatchTest) {
   DeltaState state;
   GenerateDeltaFile(false,
                     false,
@@ -1021,7 +1058,7 @@
                     kSourceMinorPayloadVersion);
 }
 
-TEST(DeltaPerformerIntegrationTest, RunAsRootSmallImageChunksTest) {
+TEST_F(DeltaPerformerIntegrationTest, RunAsRootSmallImageChunksTest) {
   DoSmallImageTest(false,
                    false,
                    kBlockSize,
@@ -1030,27 +1067,28 @@
                    kSourceMinorPayloadVersion);
 }
 
-TEST(DeltaPerformerIntegrationTest, RunAsRootFullKernelSmallImageTest) {
+TEST_F(DeltaPerformerIntegrationTest, RunAsRootFullKernelSmallImageTest) {
   DoSmallImageTest(
       true, false, -1, kSignatureGenerator, false, kSourceMinorPayloadVersion);
 }
 
-TEST(DeltaPerformerIntegrationTest, RunAsRootFullSmallImageTest) {
+TEST_F(DeltaPerformerIntegrationTest, RunAsRootFullSmallImageTest) {
   DoSmallImageTest(
       true, true, -1, kSignatureGenerator, true, kFullPayloadMinorVersion);
 }
 
-TEST(DeltaPerformerIntegrationTest, RunAsRootSmallImageSignNoneTest) {
+TEST_F(DeltaPerformerIntegrationTest, RunAsRootSmallImageSignNoneTest) {
   DoSmallImageTest(
       false, false, -1, kSignatureNone, false, kSourceMinorPayloadVersion);
 }
 
-TEST(DeltaPerformerIntegrationTest, RunAsRootSmallImageSignGeneratedTest) {
+TEST_F(DeltaPerformerIntegrationTest, RunAsRootSmallImageSignGeneratedTest) {
   DoSmallImageTest(
       false, false, -1, kSignatureGenerated, true, kSourceMinorPayloadVersion);
 }
 
-TEST(DeltaPerformerIntegrationTest, RunAsRootSmallImageSignGeneratedShellTest) {
+TEST_F(DeltaPerformerIntegrationTest,
+       RunAsRootSmallImageSignGeneratedShellTest) {
   DoSmallImageTest(false,
                    false,
                    -1,
@@ -1059,8 +1097,8 @@
                    kSourceMinorPayloadVersion);
 }
 
-TEST(DeltaPerformerIntegrationTest,
-     RunAsRootSmallImageSignGeneratedShellECKeyTest) {
+TEST_F(DeltaPerformerIntegrationTest,
+       RunAsRootSmallImageSignGeneratedShellECKeyTest) {
   DoSmallImageTest(false,
                    false,
                    -1,
@@ -1069,8 +1107,8 @@
                    kSourceMinorPayloadVersion);
 }
 
-TEST(DeltaPerformerIntegrationTest,
-     RunAsRootSmallImageSignGeneratedShellBadKeyTest) {
+TEST_F(DeltaPerformerIntegrationTest,
+       RunAsRootSmallImageSignGeneratedShellBadKeyTest) {
   DoSmallImageTest(false,
                    false,
                    -1,
@@ -1079,8 +1117,8 @@
                    kSourceMinorPayloadVersion);
 }
 
-TEST(DeltaPerformerIntegrationTest,
-     RunAsRootSmallImageSignGeneratedShellRotateCl1Test) {
+TEST_F(DeltaPerformerIntegrationTest,
+       RunAsRootSmallImageSignGeneratedShellRotateCl1Test) {
   DoSmallImageTest(false,
                    false,
                    -1,
@@ -1089,8 +1127,8 @@
                    kSourceMinorPayloadVersion);
 }
 
-TEST(DeltaPerformerIntegrationTest,
-     RunAsRootSmallImageSignGeneratedShellRotateCl2Test) {
+TEST_F(DeltaPerformerIntegrationTest,
+       RunAsRootSmallImageSignGeneratedShellRotateCl2Test) {
   DoSmallImageTest(false,
                    false,
                    -1,
@@ -1099,14 +1137,97 @@
                    kSourceMinorPayloadVersion);
 }
 
-TEST(DeltaPerformerIntegrationTest, RunAsRootSmallImageSourceOpsTest) {
+TEST_F(DeltaPerformerIntegrationTest, RunAsRootSmallImageSourceOpsTest) {
   DoSmallImageTest(
       false, false, -1, kSignatureGenerator, false, kSourceMinorPayloadVersion);
 }
 
-TEST(DeltaPerformerIntegrationTest,
-     RunAsRootMandatoryOperationHashMismatchTest) {
+TEST_F(DeltaPerformerIntegrationTest,
+       RunAsRootMandatoryOperationHashMismatchTest) {
   DoOperationHashMismatchTest(kInvalidOperationData, true);
 }
 
+TEST_F(DeltaPerformerIntegrationTest, ValidatePerPartitionTimestampSuccess) {
+  // The Manifest we are validating.
+  DeltaArchiveManifest manifest;
+
+  fake_hardware_.SetVersion("system", "5");
+  fake_hardware_.SetVersion("product", "99");
+  fake_hardware_.SetBuildTimestamp(1);
+
+  manifest.set_minor_version(kFullPayloadMinorVersion);
+  manifest.set_max_timestamp(2);
+  AddPartition(&manifest, "system", 10);
+  AddPartition(&manifest, "product", 100);
+
+  RunManifestValidation(
+      manifest, kMaxSupportedMajorPayloadVersion, ErrorCode::kSuccess);
+}
+
+TEST_F(DeltaPerformerIntegrationTest, ValidatePerPartitionTimestampFailure) {
+  // The Manifest we are validating.
+  DeltaArchiveManifest manifest;
+
+  fake_hardware_.SetVersion("system", "5");
+  fake_hardware_.SetVersion("product", "99");
+  fake_hardware_.SetBuildTimestamp(1);
+
+  manifest.set_minor_version(kFullPayloadMinorVersion);
+  manifest.set_max_timestamp(2);
+  AddPartition(&manifest, "system", 10);
+  AddPartition(&manifest, "product", 98);
+
+  RunManifestValidation(manifest,
+                        kMaxSupportedMajorPayloadVersion,
+                        ErrorCode::kPayloadTimestampError);
+}
+
+TEST_F(DeltaPerformerIntegrationTest,
+       ValidatePerPartitionTimestampMissingTimestamp) {
+  // The Manifest we are validating.
+  DeltaArchiveManifest manifest;
+
+  fake_hardware_.SetVersion("system", "5");
+  fake_hardware_.SetVersion("product", "99");
+  fake_hardware_.SetBuildTimestamp(1);
+
+  manifest.set_minor_version(kFullPayloadMinorVersion);
+  manifest.set_max_timestamp(2);
+  AddPartition(&manifest, "system", 10);
+  {
+    auto& partition = *manifest.add_partitions();
+    // For complete updates, missing timestamp should not trigger
+    // timestamp error.
+    partition.set_partition_name("product");
+  }
+
+  RunManifestValidation(
+      manifest, kMaxSupportedMajorPayloadVersion, ErrorCode::kSuccess);
+}
+
+TEST_F(DeltaPerformerIntegrationTest,
+       ValidatePerPartitionTimestampPartialUpdate) {
+  // The Manifest we are validating.
+  DeltaArchiveManifest manifest;
+
+  fake_hardware_.SetVersion("system", "5");
+  fake_hardware_.SetVersion("product", "99");
+  fake_hardware_.SetBuildTimestamp(1);
+
+  manifest.set_minor_version(kPartialUpdateMinorPayloadVersion);
+  manifest.set_max_timestamp(2);
+  manifest.set_partial_update(true);
+  AddPartition(&manifest, "system", 10);
+  {
+    auto& partition = *manifest.add_partitions();
+    // For partial updates, missing timestamp should
+    // trigger an error
+    partition.set_partition_name("product");
+  }
+
+  RunManifestValidation(manifest,
+                        kMaxSupportedMajorPayloadVersion,
+                        ErrorCode::kPayloadTimestampError);
+}
+
 }  // namespace chromeos_update_engine
diff --git a/payload_consumer/delta_performer_unittest.cc b/payload_consumer/delta_performer_unittest.cc
index 44107cd..fbd754f 100644
--- a/payload_consumer/delta_performer_unittest.cc
+++ b/payload_consumer/delta_performer_unittest.cc
@@ -36,9 +36,11 @@
 #include <gtest/gtest.h>
 
 #include "update_engine/common/constants.h"
+#include "update_engine/common/error_code.h"
 #include "update_engine/common/fake_boot_control.h"
 #include "update_engine/common/fake_hardware.h"
 #include "update_engine/common/fake_prefs.h"
+#include "update_engine/common/hardware_interface.h"
 #include "update_engine/common/test_utils.h"
 #include "update_engine/common/utils.h"
 #include "update_engine/payload_consumer/fake_file_descriptor.h"
@@ -899,6 +901,24 @@
                         ErrorCode::kPayloadTimestampError);
 }
 
+TEST_F(DeltaPerformerTest, ValidatePerPartitionTimestampSuccess) {
+  // The Manifest we are validating.
+  DeltaArchiveManifest manifest;
+
+  manifest.set_minor_version(kFullPayloadMinorVersion);
+  manifest.set_max_timestamp(2);
+  fake_hardware_.SetBuildTimestamp(1);
+  auto& partition = *manifest.add_partitions();
+  partition.set_version("10");
+  partition.set_partition_name("system");
+  fake_hardware_.SetVersion("system", "5");
+
+  RunManifestValidation(manifest,
+                        kMaxSupportedMajorPayloadVersion,
+                        InstallPayloadType::kFull,
+                        ErrorCode::kSuccess);
+}
+
 TEST_F(DeltaPerformerTest, BrilloMetadataSignatureSizeTest) {
   unsigned int seed = time(nullptr);
   EXPECT_TRUE(performer_.Write(kDeltaMagic, sizeof(kDeltaMagic)));
diff --git a/scripts/update_payload/update_metadata_pb2.py b/scripts/update_payload/update_metadata_pb2.py
index d41c1da..841cd22 100644
--- a/scripts/update_payload/update_metadata_pb2.py
+++ b/scripts/update_payload/update_metadata_pb2.py
@@ -2,8 +2,6 @@
 # Generated by the protocol buffer compiler.  DO NOT EDIT!
 # source: update_metadata.proto
 
-import sys
-_b=sys.version_info[0]<3 and (lambda x:x) or (lambda x:x.encode('latin1'))
 from google.protobuf import descriptor as _descriptor
 from google.protobuf import message as _message
 from google.protobuf import reflection as _reflection
@@ -19,8 +17,8 @@
   name='update_metadata.proto',
   package='chromeos_update_engine',
   syntax='proto2',
-  serialized_options=_b('H\003'),
-  serialized_pb=_b('\n\x15update_metadata.proto\x12\x16\x63hromeos_update_engine\"1\n\x06\x45xtent\x12\x13\n\x0bstart_block\x18\x01 \x01(\x04\x12\x12\n\nnum_blocks\x18\x02 \x01(\x04\"\x9f\x01\n\nSignatures\x12@\n\nsignatures\x18\x01 \x03(\x0b\x32,.chromeos_update_engine.Signatures.Signature\x1aO\n\tSignature\x12\x13\n\x07version\x18\x01 \x01(\rB\x02\x18\x01\x12\x0c\n\x04\x64\x61ta\x18\x02 \x01(\x0c\x12\x1f\n\x17unpadded_signature_size\x18\x03 \x01(\x07\"+\n\rPartitionInfo\x12\x0c\n\x04size\x18\x01 \x01(\x04\x12\x0c\n\x04hash\x18\x02 \x01(\x0c\"w\n\tImageInfo\x12\r\n\x05\x62oard\x18\x01 \x01(\t\x12\x0b\n\x03key\x18\x02 \x01(\t\x12\x0f\n\x07\x63hannel\x18\x03 \x01(\t\x12\x0f\n\x07version\x18\x04 \x01(\t\x12\x15\n\rbuild_channel\x18\x05 \x01(\t\x12\x15\n\rbuild_version\x18\x06 \x01(\t\"\xee\x03\n\x10InstallOperation\x12;\n\x04type\x18\x01 \x02(\x0e\x32-.chromeos_update_engine.InstallOperation.Type\x12\x13\n\x0b\x64\x61ta_offset\x18\x02 \x01(\x04\x12\x13\n\x0b\x64\x61ta_length\x18\x03 \x01(\x04\x12\x33\n\x0bsrc_extents\x18\x04 \x03(\x0b\x32\x1e.chromeos_update_engine.Extent\x12\x12\n\nsrc_length\x18\x05 \x01(\x04\x12\x33\n\x0b\x64st_extents\x18\x06 \x03(\x0b\x32\x1e.chromeos_update_engine.Extent\x12\x12\n\ndst_length\x18\x07 \x01(\x04\x12\x18\n\x10\x64\x61ta_sha256_hash\x18\x08 \x01(\x0c\x12\x17\n\x0fsrc_sha256_hash\x18\t \x01(\x0c\"\xad\x01\n\x04Type\x12\x0b\n\x07REPLACE\x10\x00\x12\x0e\n\nREPLACE_BZ\x10\x01\x12\x0c\n\x04MOVE\x10\x02\x1a\x02\x08\x01\x12\x0e\n\x06\x42SDIFF\x10\x03\x1a\x02\x08\x01\x12\x0f\n\x0bSOURCE_COPY\x10\x04\x12\x11\n\rSOURCE_BSDIFF\x10\x05\x12\x0e\n\nREPLACE_XZ\x10\x08\x12\x08\n\x04ZERO\x10\x06\x12\x0b\n\x07\x44ISCARD\x10\x07\x12\x11\n\rBROTLI_BSDIFF\x10\n\x12\x0c\n\x08PUFFDIFF\x10\t\"\xd7\x05\n\x0fPartitionUpdate\x12\x16\n\x0epartition_name\x18\x01 \x02(\t\x12\x17\n\x0frun_postinstall\x18\x02 \x01(\x08\x12\x18\n\x10postinstall_path\x18\x03 \x01(\t\x12\x17\n\x0f\x66ilesystem_type\x18\x04 \x01(\t\x12M\n\x17new_partition_signature\x18\x05 \x03(\x0b\x32,.chromeos_update_engine.Signatures.Signature\x12\x41\n\x12old_partition_info\x18\x06 \x01(\x0b\x32%.chromeos_update_engine.PartitionInfo\x12\x41\n\x12new_partition_info\x18\x07 \x01(\x0b\x32%.chromeos_update_engine.PartitionInfo\x12<\n\noperations\x18\x08 \x03(\x0b\x32(.chromeos_update_engine.InstallOperation\x12\x1c\n\x14postinstall_optional\x18\t \x01(\x08\x12=\n\x15hash_tree_data_extent\x18\n \x01(\x0b\x32\x1e.chromeos_update_engine.Extent\x12\x38\n\x10hash_tree_extent\x18\x0b \x01(\x0b\x32\x1e.chromeos_update_engine.Extent\x12\x1b\n\x13hash_tree_algorithm\x18\x0c \x01(\t\x12\x16\n\x0ehash_tree_salt\x18\r \x01(\x0c\x12\x37\n\x0f\x66\x65\x63_data_extent\x18\x0e \x01(\x0b\x32\x1e.chromeos_update_engine.Extent\x12\x32\n\nfec_extent\x18\x0f \x01(\x0b\x32\x1e.chromeos_update_engine.Extent\x12\x14\n\tfec_roots\x18\x10 \x01(\r:\x01\x32\"L\n\x15\x44ynamicPartitionGroup\x12\x0c\n\x04name\x18\x01 \x02(\t\x12\x0c\n\x04size\x18\x02 \x01(\x04\x12\x17\n\x0fpartition_names\x18\x03 \x03(\t\"s\n\x18\x44ynamicPartitionMetadata\x12=\n\x06groups\x18\x01 \x03(\x0b\x32-.chromeos_update_engine.DynamicPartitionGroup\x12\x18\n\x10snapshot_enabled\x18\x02 \x01(\x08\"\xe1\x06\n\x14\x44\x65ltaArchiveManifest\x12H\n\x12install_operations\x18\x01 \x03(\x0b\x32(.chromeos_update_engine.InstallOperationB\x02\x18\x01\x12O\n\x19kernel_install_operations\x18\x02 \x03(\x0b\x32(.chromeos_update_engine.InstallOperationB\x02\x18\x01\x12\x18\n\nblock_size\x18\x03 \x01(\r:\x04\x34\x30\x39\x36\x12\x19\n\x11signatures_offset\x18\x04 \x01(\x04\x12\x17\n\x0fsignatures_size\x18\x05 \x01(\x04\x12\x42\n\x0fold_kernel_info\x18\x06 \x01(\x0b\x32%.chromeos_update_engine.PartitionInfoB\x02\x18\x01\x12\x42\n\x0fnew_kernel_info\x18\x07 \x01(\x0b\x32%.chromeos_update_engine.PartitionInfoB\x02\x18\x01\x12\x42\n\x0fold_rootfs_info\x18\x08 \x01(\x0b\x32%.chromeos_update_engine.PartitionInfoB\x02\x18\x01\x12\x42\n\x0fnew_rootfs_info\x18\t \x01(\x0b\x32%.chromeos_update_engine.PartitionInfoB\x02\x18\x01\x12\x39\n\x0eold_image_info\x18\n \x01(\x0b\x32!.chromeos_update_engine.ImageInfo\x12\x39\n\x0enew_image_info\x18\x0b \x01(\x0b\x32!.chromeos_update_engine.ImageInfo\x12\x18\n\rminor_version\x18\x0c \x01(\r:\x01\x30\x12;\n\npartitions\x18\r \x03(\x0b\x32\'.chromeos_update_engine.PartitionUpdate\x12\x15\n\rmax_timestamp\x18\x0e \x01(\x03\x12T\n\x1a\x64ynamic_partition_metadata\x18\x0f \x01(\x0b\x32\x30.chromeos_update_engine.DynamicPartitionMetadata\x12\x16\n\x0epartial_update\x18\x10 \x01(\x08\x42\x02H\x03')
+  serialized_options=b'H\003',
+  serialized_pb=b'\n\x15update_metadata.proto\x12\x16\x63hromeos_update_engine\"1\n\x06\x45xtent\x12\x13\n\x0bstart_block\x18\x01 \x01(\x04\x12\x12\n\nnum_blocks\x18\x02 \x01(\x04\"\x9f\x01\n\nSignatures\x12@\n\nsignatures\x18\x01 \x03(\x0b\x32,.chromeos_update_engine.Signatures.Signature\x1aO\n\tSignature\x12\x13\n\x07version\x18\x01 \x01(\rB\x02\x18\x01\x12\x0c\n\x04\x64\x61ta\x18\x02 \x01(\x0c\x12\x1f\n\x17unpadded_signature_size\x18\x03 \x01(\x07\"+\n\rPartitionInfo\x12\x0c\n\x04size\x18\x01 \x01(\x04\x12\x0c\n\x04hash\x18\x02 \x01(\x0c\"w\n\tImageInfo\x12\r\n\x05\x62oard\x18\x01 \x01(\t\x12\x0b\n\x03key\x18\x02 \x01(\t\x12\x0f\n\x07\x63hannel\x18\x03 \x01(\t\x12\x0f\n\x07version\x18\x04 \x01(\t\x12\x15\n\rbuild_channel\x18\x05 \x01(\t\x12\x15\n\rbuild_version\x18\x06 \x01(\t\"\xee\x03\n\x10InstallOperation\x12;\n\x04type\x18\x01 \x02(\x0e\x32-.chromeos_update_engine.InstallOperation.Type\x12\x13\n\x0b\x64\x61ta_offset\x18\x02 \x01(\x04\x12\x13\n\x0b\x64\x61ta_length\x18\x03 \x01(\x04\x12\x33\n\x0bsrc_extents\x18\x04 \x03(\x0b\x32\x1e.chromeos_update_engine.Extent\x12\x12\n\nsrc_length\x18\x05 \x01(\x04\x12\x33\n\x0b\x64st_extents\x18\x06 \x03(\x0b\x32\x1e.chromeos_update_engine.Extent\x12\x12\n\ndst_length\x18\x07 \x01(\x04\x12\x18\n\x10\x64\x61ta_sha256_hash\x18\x08 \x01(\x0c\x12\x17\n\x0fsrc_sha256_hash\x18\t \x01(\x0c\"\xad\x01\n\x04Type\x12\x0b\n\x07REPLACE\x10\x00\x12\x0e\n\nREPLACE_BZ\x10\x01\x12\x0c\n\x04MOVE\x10\x02\x1a\x02\x08\x01\x12\x0e\n\x06\x42SDIFF\x10\x03\x1a\x02\x08\x01\x12\x0f\n\x0bSOURCE_COPY\x10\x04\x12\x11\n\rSOURCE_BSDIFF\x10\x05\x12\x0e\n\nREPLACE_XZ\x10\x08\x12\x08\n\x04ZERO\x10\x06\x12\x0b\n\x07\x44ISCARD\x10\x07\x12\x11\n\rBROTLI_BSDIFF\x10\n\x12\x0c\n\x08PUFFDIFF\x10\t\"\xe8\x05\n\x0fPartitionUpdate\x12\x16\n\x0epartition_name\x18\x01 \x02(\t\x12\x17\n\x0frun_postinstall\x18\x02 \x01(\x08\x12\x18\n\x10postinstall_path\x18\x03 \x01(\t\x12\x17\n\x0f\x66ilesystem_type\x18\x04 \x01(\t\x12M\n\x17new_partition_signature\x18\x05 \x03(\x0b\x32,.chromeos_update_engine.Signatures.Signature\x12\x41\n\x12old_partition_info\x18\x06 \x01(\x0b\x32%.chromeos_update_engine.PartitionInfo\x12\x41\n\x12new_partition_info\x18\x07 \x01(\x0b\x32%.chromeos_update_engine.PartitionInfo\x12<\n\noperations\x18\x08 \x03(\x0b\x32(.chromeos_update_engine.InstallOperation\x12\x1c\n\x14postinstall_optional\x18\t \x01(\x08\x12=\n\x15hash_tree_data_extent\x18\n \x01(\x0b\x32\x1e.chromeos_update_engine.Extent\x12\x38\n\x10hash_tree_extent\x18\x0b \x01(\x0b\x32\x1e.chromeos_update_engine.Extent\x12\x1b\n\x13hash_tree_algorithm\x18\x0c \x01(\t\x12\x16\n\x0ehash_tree_salt\x18\r \x01(\x0c\x12\x37\n\x0f\x66\x65\x63_data_extent\x18\x0e \x01(\x0b\x32\x1e.chromeos_update_engine.Extent\x12\x32\n\nfec_extent\x18\x0f \x01(\x0b\x32\x1e.chromeos_update_engine.Extent\x12\x14\n\tfec_roots\x18\x10 \x01(\r:\x01\x32\x12\x0f\n\x07version\x18\x11 \x01(\t\"L\n\x15\x44ynamicPartitionGroup\x12\x0c\n\x04name\x18\x01 \x02(\t\x12\x0c\n\x04size\x18\x02 \x01(\x04\x12\x17\n\x0fpartition_names\x18\x03 \x03(\t\"s\n\x18\x44ynamicPartitionMetadata\x12=\n\x06groups\x18\x01 \x03(\x0b\x32-.chromeos_update_engine.DynamicPartitionGroup\x12\x18\n\x10snapshot_enabled\x18\x02 \x01(\x08\"\xe1\x06\n\x14\x44\x65ltaArchiveManifest\x12H\n\x12install_operations\x18\x01 \x03(\x0b\x32(.chromeos_update_engine.InstallOperationB\x02\x18\x01\x12O\n\x19kernel_install_operations\x18\x02 \x03(\x0b\x32(.chromeos_update_engine.InstallOperationB\x02\x18\x01\x12\x18\n\nblock_size\x18\x03 \x01(\r:\x04\x34\x30\x39\x36\x12\x19\n\x11signatures_offset\x18\x04 \x01(\x04\x12\x17\n\x0fsignatures_size\x18\x05 \x01(\x04\x12\x42\n\x0fold_kernel_info\x18\x06 \x01(\x0b\x32%.chromeos_update_engine.PartitionInfoB\x02\x18\x01\x12\x42\n\x0fnew_kernel_info\x18\x07 \x01(\x0b\x32%.chromeos_update_engine.PartitionInfoB\x02\x18\x01\x12\x42\n\x0fold_rootfs_info\x18\x08 \x01(\x0b\x32%.chromeos_update_engine.PartitionInfoB\x02\x18\x01\x12\x42\n\x0fnew_rootfs_info\x18\t \x01(\x0b\x32%.chromeos_update_engine.PartitionInfoB\x02\x18\x01\x12\x39\n\x0eold_image_info\x18\n \x01(\x0b\x32!.chromeos_update_engine.ImageInfo\x12\x39\n\x0enew_image_info\x18\x0b \x01(\x0b\x32!.chromeos_update_engine.ImageInfo\x12\x18\n\rminor_version\x18\x0c \x01(\r:\x01\x30\x12;\n\npartitions\x18\r \x03(\x0b\x32\'.chromeos_update_engine.PartitionUpdate\x12\x15\n\rmax_timestamp\x18\x0e \x01(\x03\x12T\n\x1a\x64ynamic_partition_metadata\x18\x0f \x01(\x0b\x32\x30.chromeos_update_engine.DynamicPartitionMetadata\x12\x16\n\x0epartial_update\x18\x10 \x01(\x08\x42\x02H\x03'
 )
 
 
@@ -41,11 +39,11 @@
       type=None),
     _descriptor.EnumValueDescriptor(
       name='MOVE', index=2, number=2,
-      serialized_options=_b('\010\001'),
+      serialized_options=b'\010\001',
       type=None),
     _descriptor.EnumValueDescriptor(
       name='BSDIFF', index=3, number=3,
-      serialized_options=_b('\010\001'),
+      serialized_options=b'\010\001',
       type=None),
     _descriptor.EnumValueDescriptor(
       name='SOURCE_COPY', index=4, number=4,
@@ -135,11 +133,11 @@
       has_default_value=False, default_value=0,
       message_type=None, enum_type=None, containing_type=None,
       is_extension=False, extension_scope=None,
-      serialized_options=_b('\030\001'), file=DESCRIPTOR),
+      serialized_options=b'\030\001', file=DESCRIPTOR),
     _descriptor.FieldDescriptor(
       name='data', full_name='chromeos_update_engine.Signatures.Signature.data', index=1,
       number=2, type=12, cpp_type=9, label=1,
-      has_default_value=False, default_value=_b(""),
+      has_default_value=False, default_value=b"",
       message_type=None, enum_type=None, containing_type=None,
       is_extension=False, extension_scope=None,
       serialized_options=None, file=DESCRIPTOR),
@@ -214,7 +212,7 @@
     _descriptor.FieldDescriptor(
       name='hash', full_name='chromeos_update_engine.PartitionInfo.hash', index=1,
       number=2, type=12, cpp_type=9, label=1,
-      has_default_value=False, default_value=_b(""),
+      has_default_value=False, default_value=b"",
       message_type=None, enum_type=None, containing_type=None,
       is_extension=False, extension_scope=None,
       serialized_options=None, file=DESCRIPTOR),
@@ -245,42 +243,42 @@
     _descriptor.FieldDescriptor(
       name='board', full_name='chromeos_update_engine.ImageInfo.board', index=0,
       number=1, type=9, cpp_type=9, label=1,
-      has_default_value=False, default_value=_b("").decode('utf-8'),
+      has_default_value=False, default_value=b"".decode('utf-8'),
       message_type=None, enum_type=None, containing_type=None,
       is_extension=False, extension_scope=None,
       serialized_options=None, file=DESCRIPTOR),
     _descriptor.FieldDescriptor(
       name='key', full_name='chromeos_update_engine.ImageInfo.key', index=1,
       number=2, type=9, cpp_type=9, label=1,
-      has_default_value=False, default_value=_b("").decode('utf-8'),
+      has_default_value=False, default_value=b"".decode('utf-8'),
       message_type=None, enum_type=None, containing_type=None,
       is_extension=False, extension_scope=None,
       serialized_options=None, file=DESCRIPTOR),
     _descriptor.FieldDescriptor(
       name='channel', full_name='chromeos_update_engine.ImageInfo.channel', index=2,
       number=3, type=9, cpp_type=9, label=1,
-      has_default_value=False, default_value=_b("").decode('utf-8'),
+      has_default_value=False, default_value=b"".decode('utf-8'),
       message_type=None, enum_type=None, containing_type=None,
       is_extension=False, extension_scope=None,
       serialized_options=None, file=DESCRIPTOR),
     _descriptor.FieldDescriptor(
       name='version', full_name='chromeos_update_engine.ImageInfo.version', index=3,
       number=4, type=9, cpp_type=9, label=1,
-      has_default_value=False, default_value=_b("").decode('utf-8'),
+      has_default_value=False, default_value=b"".decode('utf-8'),
       message_type=None, enum_type=None, containing_type=None,
       is_extension=False, extension_scope=None,
       serialized_options=None, file=DESCRIPTOR),
     _descriptor.FieldDescriptor(
       name='build_channel', full_name='chromeos_update_engine.ImageInfo.build_channel', index=4,
       number=5, type=9, cpp_type=9, label=1,
-      has_default_value=False, default_value=_b("").decode('utf-8'),
+      has_default_value=False, default_value=b"".decode('utf-8'),
       message_type=None, enum_type=None, containing_type=None,
       is_extension=False, extension_scope=None,
       serialized_options=None, file=DESCRIPTOR),
     _descriptor.FieldDescriptor(
       name='build_version', full_name='chromeos_update_engine.ImageInfo.build_version', index=5,
       number=6, type=9, cpp_type=9, label=1,
-      has_default_value=False, default_value=_b("").decode('utf-8'),
+      has_default_value=False, default_value=b"".decode('utf-8'),
       message_type=None, enum_type=None, containing_type=None,
       is_extension=False, extension_scope=None,
       serialized_options=None, file=DESCRIPTOR),
@@ -360,14 +358,14 @@
     _descriptor.FieldDescriptor(
       name='data_sha256_hash', full_name='chromeos_update_engine.InstallOperation.data_sha256_hash', index=7,
       number=8, type=12, cpp_type=9, label=1,
-      has_default_value=False, default_value=_b(""),
+      has_default_value=False, default_value=b"",
       message_type=None, enum_type=None, containing_type=None,
       is_extension=False, extension_scope=None,
       serialized_options=None, file=DESCRIPTOR),
     _descriptor.FieldDescriptor(
       name='src_sha256_hash', full_name='chromeos_update_engine.InstallOperation.src_sha256_hash', index=8,
       number=9, type=12, cpp_type=9, label=1,
-      has_default_value=False, default_value=_b(""),
+      has_default_value=False, default_value=b"",
       message_type=None, enum_type=None, containing_type=None,
       is_extension=False, extension_scope=None,
       serialized_options=None, file=DESCRIPTOR),
@@ -399,7 +397,7 @@
     _descriptor.FieldDescriptor(
       name='partition_name', full_name='chromeos_update_engine.PartitionUpdate.partition_name', index=0,
       number=1, type=9, cpp_type=9, label=2,
-      has_default_value=False, default_value=_b("").decode('utf-8'),
+      has_default_value=False, default_value=b"".decode('utf-8'),
       message_type=None, enum_type=None, containing_type=None,
       is_extension=False, extension_scope=None,
       serialized_options=None, file=DESCRIPTOR),
@@ -413,14 +411,14 @@
     _descriptor.FieldDescriptor(
       name='postinstall_path', full_name='chromeos_update_engine.PartitionUpdate.postinstall_path', index=2,
       number=3, type=9, cpp_type=9, label=1,
-      has_default_value=False, default_value=_b("").decode('utf-8'),
+      has_default_value=False, default_value=b"".decode('utf-8'),
       message_type=None, enum_type=None, containing_type=None,
       is_extension=False, extension_scope=None,
       serialized_options=None, file=DESCRIPTOR),
     _descriptor.FieldDescriptor(
       name='filesystem_type', full_name='chromeos_update_engine.PartitionUpdate.filesystem_type', index=3,
       number=4, type=9, cpp_type=9, label=1,
-      has_default_value=False, default_value=_b("").decode('utf-8'),
+      has_default_value=False, default_value=b"".decode('utf-8'),
       message_type=None, enum_type=None, containing_type=None,
       is_extension=False, extension_scope=None,
       serialized_options=None, file=DESCRIPTOR),
@@ -476,14 +474,14 @@
     _descriptor.FieldDescriptor(
       name='hash_tree_algorithm', full_name='chromeos_update_engine.PartitionUpdate.hash_tree_algorithm', index=11,
       number=12, type=9, cpp_type=9, label=1,
-      has_default_value=False, default_value=_b("").decode('utf-8'),
+      has_default_value=False, default_value=b"".decode('utf-8'),
       message_type=None, enum_type=None, containing_type=None,
       is_extension=False, extension_scope=None,
       serialized_options=None, file=DESCRIPTOR),
     _descriptor.FieldDescriptor(
       name='hash_tree_salt', full_name='chromeos_update_engine.PartitionUpdate.hash_tree_salt', index=12,
       number=13, type=12, cpp_type=9, label=1,
-      has_default_value=False, default_value=_b(""),
+      has_default_value=False, default_value=b"",
       message_type=None, enum_type=None, containing_type=None,
       is_extension=False, extension_scope=None,
       serialized_options=None, file=DESCRIPTOR),
@@ -508,6 +506,13 @@
       message_type=None, enum_type=None, containing_type=None,
       is_extension=False, extension_scope=None,
       serialized_options=None, file=DESCRIPTOR),
+    _descriptor.FieldDescriptor(
+      name='version', full_name='chromeos_update_engine.PartitionUpdate.version', index=16,
+      number=17, type=9, cpp_type=9, label=1,
+      has_default_value=False, default_value=b"".decode('utf-8'),
+      message_type=None, enum_type=None, containing_type=None,
+      is_extension=False, extension_scope=None,
+      serialized_options=None, file=DESCRIPTOR),
   ],
   extensions=[
   ],
@@ -521,7 +526,7 @@
   oneofs=[
   ],
   serialized_start=926,
-  serialized_end=1653,
+  serialized_end=1670,
 )
 
 
@@ -535,7 +540,7 @@
     _descriptor.FieldDescriptor(
       name='name', full_name='chromeos_update_engine.DynamicPartitionGroup.name', index=0,
       number=1, type=9, cpp_type=9, label=2,
-      has_default_value=False, default_value=_b("").decode('utf-8'),
+      has_default_value=False, default_value=b"".decode('utf-8'),
       message_type=None, enum_type=None, containing_type=None,
       is_extension=False, extension_scope=None,
       serialized_options=None, file=DESCRIPTOR),
@@ -565,8 +570,8 @@
   extension_ranges=[],
   oneofs=[
   ],
-  serialized_start=1655,
-  serialized_end=1731,
+  serialized_start=1672,
+  serialized_end=1748,
 )
 
 
@@ -603,8 +608,8 @@
   extension_ranges=[],
   oneofs=[
   ],
-  serialized_start=1733,
-  serialized_end=1848,
+  serialized_start=1750,
+  serialized_end=1865,
 )
 
 
@@ -621,14 +626,14 @@
       has_default_value=False, default_value=[],
       message_type=None, enum_type=None, containing_type=None,
       is_extension=False, extension_scope=None,
-      serialized_options=_b('\030\001'), file=DESCRIPTOR),
+      serialized_options=b'\030\001', file=DESCRIPTOR),
     _descriptor.FieldDescriptor(
       name='kernel_install_operations', full_name='chromeos_update_engine.DeltaArchiveManifest.kernel_install_operations', index=1,
       number=2, type=11, cpp_type=10, label=3,
       has_default_value=False, default_value=[],
       message_type=None, enum_type=None, containing_type=None,
       is_extension=False, extension_scope=None,
-      serialized_options=_b('\030\001'), file=DESCRIPTOR),
+      serialized_options=b'\030\001', file=DESCRIPTOR),
     _descriptor.FieldDescriptor(
       name='block_size', full_name='chromeos_update_engine.DeltaArchiveManifest.block_size', index=2,
       number=3, type=13, cpp_type=3, label=1,
@@ -656,28 +661,28 @@
       has_default_value=False, default_value=None,
       message_type=None, enum_type=None, containing_type=None,
       is_extension=False, extension_scope=None,
-      serialized_options=_b('\030\001'), file=DESCRIPTOR),
+      serialized_options=b'\030\001', file=DESCRIPTOR),
     _descriptor.FieldDescriptor(
       name='new_kernel_info', full_name='chromeos_update_engine.DeltaArchiveManifest.new_kernel_info', index=6,
       number=7, type=11, cpp_type=10, label=1,
       has_default_value=False, default_value=None,
       message_type=None, enum_type=None, containing_type=None,
       is_extension=False, extension_scope=None,
-      serialized_options=_b('\030\001'), file=DESCRIPTOR),
+      serialized_options=b'\030\001', file=DESCRIPTOR),
     _descriptor.FieldDescriptor(
       name='old_rootfs_info', full_name='chromeos_update_engine.DeltaArchiveManifest.old_rootfs_info', index=7,
       number=8, type=11, cpp_type=10, label=1,
       has_default_value=False, default_value=None,
       message_type=None, enum_type=None, containing_type=None,
       is_extension=False, extension_scope=None,
-      serialized_options=_b('\030\001'), file=DESCRIPTOR),
+      serialized_options=b'\030\001', file=DESCRIPTOR),
     _descriptor.FieldDescriptor(
       name='new_rootfs_info', full_name='chromeos_update_engine.DeltaArchiveManifest.new_rootfs_info', index=8,
       number=9, type=11, cpp_type=10, label=1,
       has_default_value=False, default_value=None,
       message_type=None, enum_type=None, containing_type=None,
       is_extension=False, extension_scope=None,
-      serialized_options=_b('\030\001'), file=DESCRIPTOR),
+      serialized_options=b'\030\001', file=DESCRIPTOR),
     _descriptor.FieldDescriptor(
       name='old_image_info', full_name='chromeos_update_engine.DeltaArchiveManifest.old_image_info', index=9,
       number=10, type=11, cpp_type=10, label=1,
@@ -739,8 +744,8 @@
   extension_ranges=[],
   oneofs=[
   ],
-  serialized_start=1851,
-  serialized_end=2716,
+  serialized_start=1868,
+  serialized_end=2733,
 )
 
 _SIGNATURES_SIGNATURE.containing_type = _SIGNATURES
diff --git a/update_metadata.proto b/update_metadata.proto
index e6a067e..f79e38b 100644
--- a/update_metadata.proto
+++ b/update_metadata.proto
@@ -288,6 +288,11 @@
 
   // The number of FEC roots.
   optional uint32 fec_roots = 16 [default = 2];
+
+  // Per-partition version used for downgrade detection, added
+  // as an effort to support partial updates. For most partitions,
+  // this is the build timestamp.
+  optional string version = 17;
 }
 
 message DynamicPartitionGroup {