diff --git a/download_action.cc b/download_action.cc
index bb5d189..c17d7e2 100644
--- a/download_action.cc
+++ b/download_action.cc
@@ -123,7 +123,10 @@
     processor_->ActionComplete(this, kActionCodeDownloadWriteError);
     return;
   }
-  omaha_hash_calculator_.Update(bytes, length);
+  // DeltaPerformer checks the hashes for delta updates.
+  if (install_plan_.is_full_update) {
+    omaha_hash_calculator_.Update(bytes, length);
+  }
 }
 
 namespace {