diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 67752149538..7d1068adfe1 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -5079,9 +5079,12 @@ ATPrepCmd(List **wqueue, Relation rel, AlterTableCmd *cmd,
 		case AT_SetNotNull:		/* ALTER COLUMN SET NOT NULL */
 			ATSimplePermissions(cmd->subtype, rel,
 								ATT_TABLE | ATT_PARTITIONED_TABLE | ATT_FOREIGN_TABLE);
-			/* Set up recursion for phase 2; no other prep needed */
 			if (recurse)
+			{
+				/* recurses at exec time; lock descendants and set flag */
+				(void) find_all_inheritors(RelationGetRelid(rel), lockmode, NULL);
 				cmd->recurse = true;
+			}
 			pass = AT_PASS_COL_ATTRS;
 			break;
 		case AT_SetExpression:	/* ALTER COLUMN SET EXPRESSION */