diff --git a/update_metadata.proto b/update_metadata.proto
index 4fe5fd3..be45f88 100644
--- a/update_metadata.proto
+++ b/update_metadata.proto
@@ -281,4 +281,8 @@
   // array can have more than two partitions if needed, and they are identified
   // by the partition name.
   repeated PartitionUpdate partitions = 13;
+
+  // The maximum timestamp of the OS allowed to apply this payload.
+  // Can be used to prevent downgrading the OS.
+  optional int64 max_timestamp = 14;
 }