diff --git a/common/fake_hardware.h b/common/fake_hardware.h
index 30c0897..30b5718 100644
--- a/common/fake_hardware.h
+++ b/common/fake_hardware.h
@@ -23,6 +23,7 @@
 
 #include <base/time/time.h>
 
+#include "update_engine/common/error_code.h"
 #include "update_engine/common/hardware_interface.h"
 #include "update_engine/common/utils.h"
 
@@ -216,8 +217,9 @@
   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 {
+  ErrorCode 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);
   }
diff --git a/common/hardware_interface.h b/common/hardware_interface.h
index 0fffbfb..b37b007 100644
--- a/common/hardware_interface.h
+++ b/common/hardware_interface.h
@@ -25,6 +25,8 @@
 #include <base/files/file_path.h>
 #include <base/time/time.h>
 
+#include "update_engine/common/error_code.h"
+
 namespace chromeos_update_engine {
 
 // The hardware interface allows access to the crossystem exposed properties,
@@ -153,8 +155,15 @@
   // 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;
+  // Return:
+  // - kSuccess if update is valid.
+  // - kPayloadTimestampError if downgrade is detected
+  // - kDownloadManifestParseError if |new_version| has an incorrect format
+  // - Other error values if the source of error is known, or kError for
+  //   a generic error on the device.
+  virtual ErrorCode 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 bbb155f..5d76f3f 100644
--- a/common/utils.cc
+++ b/common/utils.cc
@@ -990,19 +990,26 @@
   return true;
 }
 
-bool IsTimestampNewer(const std::string& old_version,
-                      const std::string& new_version) {
+ErrorCode 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;
+    return ErrorCode::kSuccess;
   }
   int64_t old_ver = 0;
-  TEST_AND_RETURN_FALSE(ParseTimestamp(old_version, &old_ver));
+  if (!ParseTimestamp(old_version, &old_ver)) {
+    return ErrorCode::kError;
+  }
   int64_t new_ver = 0;
-  TEST_AND_RETURN_FALSE(ParseTimestamp(new_version, &new_ver));
-  return old_ver <= new_ver;
+  if (!ParseTimestamp(new_version, &new_ver)) {
+    return ErrorCode::kDownloadManifestParseError;
+  }
+  if (old_ver > new_ver) {
+    return ErrorCode::kPayloadTimestampError;
+  }
+  return ErrorCode::kSuccess;
 }
 
 }  // namespace utils
diff --git a/common/utils.h b/common/utils.h
index 5dfee3b..0a1dc0c 100644
--- a/common/utils.h
+++ b/common/utils.h
@@ -324,10 +324,15 @@
 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);
+// Return kSuccess if `new_version` is larger/newer.
+// Return kSuccess if either one is empty.
+// Return kError if |old_version| is not empty and not an integer.
+// Return kDownloadManifestParseError if |new_version| is not empty and not an
+// integer.
+// Return kPayloadTimestampError if both are integers but |new_version| <
+// |old_version|.
+ErrorCode IsTimestampNewer(const std::string& old_version,
+                           const std::string& new_version);
 
 }  // namespace utils
 
diff --git a/common/utils_unittest.cc b/common/utils_unittest.cc
index 37871d2..d73b3da 100644
--- a/common/utils_unittest.cc
+++ b/common/utils_unittest.cc
@@ -482,11 +482,13 @@
 }
 
 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", ""));
+  ASSERT_EQ(ErrorCode::kPayloadTimestampError,
+            utils::IsTimestampNewer("10", "5"));
+  ASSERT_EQ(ErrorCode::kSuccess, utils::IsTimestampNewer("10", "11"));
+  ASSERT_EQ(ErrorCode::kDownloadManifestParseError,
+            utils::IsTimestampNewer("10", "lol"));
+  ASSERT_EQ(ErrorCode::kError, utils::IsTimestampNewer("lol", "ZZZ"));
+  ASSERT_EQ(ErrorCode::kSuccess, utils::IsTimestampNewer("10", ""));
 }
 
 }  // namespace chromeos_update_engine