diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
index 19be1a3995b..9086b79bc0c 100644
--- a/src/backend/access/heap/heapam.c
+++ b/src/backend/access/heap/heapam.c
@@ -5578,12 +5578,14 @@ compute_new_xmax_infomask(TransactionId xmax, uint16 old_infomask,
 				new_infomask2;
 
 	/*
-	 * TODO Move this statement to callers? REPACK (CONCURRENTLY) uses
-	 * add_to_xmax different from the current transaction when replaying data
-	 * changes. Alternatively, we can add a boolean argument to the function
-	 * indicating the special case, but that does not look nice.
-	 */
-	//Assert(TransactionIdIsCurrentTransactionId(add_to_xmax));
+	 * REPACK (CONCURRENTLY) replays data changes with the XID of the
+	 * transaction that made them (TABLE_REUSE_XID), so add_to_xmax need not
+	 * be ours.  It only replays them on tuples of the new heap that nobody
+	 * else can lock or modify and whose xmax it has not set, so xmax is
+	 * still invalid here and our own transaction does not matter below.
+	 */
+	Assert(TransactionIdIsCurrentTransactionId(add_to_xmax) ||
+		   !TransactionIdIsValid(xmax));
 
 l5:
 	new_infomask = 0;