diff --git a/tools/releasetools/ota_from_target_files.py b/tools/releasetools/ota_from_target_files.py
index c55631b556..5384699323 100755
--- a/tools/releasetools/ota_from_target_files.py
+++ b/tools/releasetools/ota_from_target_files.py
@@ -1068,10 +1068,11 @@ def GeneratePartitionTimestampFlagsDowngrade(
         pre_partition_state, post_partition_state):
   assert pre_partition_state is not None
   partition_timestamps = {}
-  for part in pre_partition_state:
-    partition_timestamps[part.partition_name] = part.version
   for part in post_partition_state:
-    partition_timestamps[part.partition_name] = \
+    partition_timestamps[part.partition_name] = part.version
+  for part in pre_partition_state:
+    if part.partition_name in partition_timestamps:
+      partition_timestamps[part.partition_name] = \
         max(part.version, partition_timestamps[part.partition_name])
   return [
       "--partition_timestamps",