diff --git a/src/backend/executor/execMain.c b/src/backend/executor/execMain.c
index ad7e2072908a54e7cd0761027c803c7bbad62512..90d37b566ae6e2549cd97077c87989a22b7798ae 100644
--- a/src/backend/executor/execMain.c
+++ b/src/backend/executor/execMain.c
@@ -817,6 +817,10 @@ InitPlan(QueryDesc *queryDesc, int eflags)
 		/* get relation's OID (will produce InvalidOid if subquery) */
 		relid = getrelid(rc->rti, rangeTable);
 
+		/*
+		 * If you change the conditions under which rel locks are acquired
+		 * here, be sure to adjust ExecOpenScanRelation to match.
+		 */
 		switch (rc->markType)
 		{
 			case ROW_MARK_EXCLUSIVE:
diff --git a/src/backend/executor/execUtils.c b/src/backend/executor/execUtils.c
index 022041bea44c159acc09ecf13994207c00bae2a1..0736d2a310254e959a0fd56077c7d0b41322e587 100644
--- a/src/backend/executor/execUtils.c
+++ b/src/backend/executor/execUtils.c
@@ -820,7 +820,9 @@ ExecOpenScanRelation(EState *estate, Index scanrelid, int eflags)
 		{
 			ExecRowMark *erm = lfirst(l);
 
-			if (erm->rti == scanrelid)
+			/* Keep this check in sync with InitPlan! */
+			if (erm->rti == scanrelid &&
+				erm->relation != NULL)
 			{
 				lockmode = NoLock;
 				break;