diff --git a/update_attempter_android.cc b/update_attempter_android.cc
index 97c53ec..08f6c20 100644
--- a/update_attempter_android.cc
+++ b/update_attempter_android.cc
@@ -750,11 +750,15 @@
         total_bytes_downloaded;
 
     int download_overhead_percentage = 0;
-    if (current_bytes_downloaded > 0) {
+    if (total_bytes_downloaded >= payload_size) {
+      CHECK_GT(payload_size, 0);
       download_overhead_percentage =
-          (total_bytes_downloaded - current_bytes_downloaded) * 100ull /
-          current_bytes_downloaded;
+          (total_bytes_downloaded - payload_size) * 100ull / payload_size;
+    } else {
+      LOG(WARNING) << "Downloaded bytes " << total_bytes_downloaded
+                   << " is smaller than the payload size " << payload_size;
     }
+
     metrics_reporter_->ReportSuccessfulUpdateMetrics(
         static_cast<int>(attempt_number),
         0,  // update abandoned count
diff --git a/update_attempter_android_unittest.cc b/update_attempter_android_unittest.cc
index 3be0b7e..721b735 100644
--- a/update_attempter_android_unittest.cc
+++ b/update_attempter_android_unittest.cc
@@ -18,6 +18,7 @@
 
 #include <memory>
 #include <string>
+#include <utility>
 
 #include <android-base/properties.h>
 #include <base/time/time.h>
@@ -57,6 +58,11 @@
     update_attempter_android_.status_ = status;
   }
 
+  void AddPayload(InstallPlan::Payload&& payload) {
+    update_attempter_android_.install_plan_.payloads.push_back(
+        std::move(payload));
+  }
+
   UpdateAttempterAndroid update_attempter_android_{
       &daemon_state_, &prefs_, &boot_control_, &hardware_};
 
@@ -143,9 +149,13 @@
       .Times(1);
   EXPECT_CALL(*metrics_reporter_,
               ReportSuccessfulUpdateMetrics(
-                  2, 0, _, _, _, _, duration, duration_uptime, 3, _))
+                  2, 0, _, 50, _, _, duration, duration_uptime, 3, _))
       .Times(1);
 
+  // Adds a payload of 50 bytes to the InstallPlan.
+  InstallPlan::Payload payload;
+  payload.size = 50;
+  AddPayload(std::move(payload));
   SetUpdateStatus(UpdateStatus::UPDATE_AVAILABLE);
   update_attempter_android_.ProcessingDone(nullptr, ErrorCode::kSuccess);
 
@@ -179,15 +189,20 @@
                   _,
                   _,
                   _,
-                  _,
+                  50,
                   test_utils::DownloadSourceMatcher(total_bytes),
-                  125,
+                  80,
                   _,
                   _,
                   _,
                   _))
       .Times(1);
 
+  // Adds a payload of 50 bytes to the InstallPlan.
+  InstallPlan::Payload payload;
+  payload.size = 50;
+  AddPayload(std::move(payload));
+
   // The first update fails after receiving 50 bytes in total.
   update_attempter_android_.BytesReceived(30, 50, 200);
   update_attempter_android_.ProcessingDone(nullptr, ErrorCode::kError);
@@ -199,7 +214,7 @@
       metrics_utils::GetPersistedValue(kPrefsTotalBytesDownloaded, &prefs_));
 
   // The second update succeeds after receiving 40 bytes, which leads to a
-  // overhead of 50 / 40 = 125%.
+  // overhead of (90 - 50) / 50 = 80%.
   update_attempter_android_.BytesReceived(40, 40, 50);
   update_attempter_android_.ProcessingDone(nullptr, ErrorCode::kSuccess);
   // Both prefs should be cleared.