diff --git a/src/backend/distributed/planner/merge_planner.c b/src/backend/distributed/planner/merge_planner.c
index 5fee6e956..8f4a6484a 100644
--- a/src/backend/distributed/planner/merge_planner.c
+++ b/src/backend/distributed/planner/merge_planner.c
@@ -1547,7 +1547,8 @@ FetchAndValidateInsertVarIfExists(Oid targetRelationId, Query *query)
 		}
 
 		/* NOT MATCHED can have either INSERT or DO NOTHING */
-		if (action->commandType == CMD_NOTHING)
+		/* NOT MATCHED BY SOURCE in PG17 can also have UPDATE */
+		if (action->commandType == CMD_NOTHING || action->commandType == CMD_UPDATE)
 		{
 			return NULL;
 		}