diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 4181c110eb7..54575fcd287 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -433,7 +433,7 @@ static AlterTableCmd *ATParseTransformCmd(List **wqueue, AlteredTableInfo *tab,
 static void ATRewriteTables(AlterTableStmt *parsetree,
 							List **wqueue, LOCKMODE lockmode,
 							AlterTableUtilityContext *context);
-static void ATRewriteTable(AlteredTableInfo *tab, Oid OIDNewHeap, LOCKMODE lockmode);
+static void ATRewriteTable(AlteredTableInfo *tab, Oid OIDNewHeap);
 static AlteredTableInfo *ATGetQueueEntry(List **wqueue, Relation rel);
 static void ATSimplePermissions(AlterTableType cmdtype, Relation rel, int allowed_targets);
 static void ATSimpleRecursion(List **wqueue, Relation rel,
@@ -5901,7 +5901,7 @@ ATRewriteTables(AlterTableStmt *parsetree, List **wqueue, LOCKMODE lockmode,
 			 * modifications, and test the current data within the table
 			 * against new constraints generated by ALTER TABLE commands.
 			 */
-			ATRewriteTable(tab, OIDNewHeap, lockmode);
+			ATRewriteTable(tab, OIDNewHeap);
 
 			/*
 			 * Swap the physical files of the old and new heaps, then rebuild
@@ -5934,7 +5934,7 @@ ATRewriteTables(AlterTableStmt *parsetree, List **wqueue, LOCKMODE lockmode,
 			 */
 			if (tab->constraints != NIL || tab->verify_new_notnull ||
 				tab->partition_constraint != NULL)
-				ATRewriteTable(tab, InvalidOid, lockmode);
+				ATRewriteTable(tab, InvalidOid);
 
 			/*
 			 * If we had SET TABLESPACE but no reason to reconstruct tuples,
@@ -6033,10 +6033,11 @@ ATRewriteTables(AlterTableStmt *parsetree, List **wqueue, LOCKMODE lockmode,
 /*
  * ATRewriteTable: scan or rewrite one table
  *
- * OIDNewHeap is InvalidOid if we don't need to rewrite
+ * A rewrite is requested by passing a valid OIDNewHeap; in that case, caller
+ * must already hold AccessExclusiveLock on it.
  */
 static void
-ATRewriteTable(AlteredTableInfo *tab, Oid OIDNewHeap, LOCKMODE lockmode)
+ATRewriteTable(AlteredTableInfo *tab, Oid OIDNewHeap)
 {
 	Relation	oldrel;
 	Relation	newrel;
@@ -6061,7 +6062,11 @@ ATRewriteTable(AlteredTableInfo *tab, Oid OIDNewHeap, LOCKMODE lockmode)
 	newTupDesc = RelationGetDescr(oldrel);	/* includes all mods */
 
 	if (OidIsValid(OIDNewHeap))
-		newrel = table_open(OIDNewHeap, lockmode);
+	{
+		Assert(CheckRelationOidLockedByMe(OIDNewHeap, AccessExclusiveLock,
+										  false));
+		newrel = table_open(OIDNewHeap, NoLock);
+	}
 	else
 		newrel = NULL;