diff --git a/src/backend/replication/pgoutput/pgoutput.c b/src/backend/replication/pgoutput/pgoutput.c
index 20d0b1e1253..2be5aaa18c4 100644
--- a/src/backend/replication/pgoutput/pgoutput.c
+++ b/src/backend/replication/pgoutput/pgoutput.c
@@ -1246,6 +1246,15 @@ pgoutput_row_filter(Relation relation, TupleTableSlot *old_slot,
 	 */
 	if (!new_slot || !old_slot)
 	{
+		/*
+		 * For UPDATE, we should only get here if the replica identity is !=
+		 * FULL and thus all the identity columns are index columns, i.e.
+		 * never TOASTed.  Therefore, we don't need to care of the unchanged
+		 * toasted replica identity columns like we do below.
+		 */
+		Assert(relation->rd_rel->relreplident != REPLICA_IDENTITY_FULL ||
+			   map_changetype_pubaction[*action] != PUBACTION_UPDATE);
+
 		ecxt->ecxt_scantuple = new_slot ? new_slot : old_slot;
 		result = pgoutput_row_filter_exec_expr(filter_exprstate, ecxt);