diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c
index e9703f1..dd27acf 100644
--- a/src/backend/storage/lmgr/lock.c
+++ b/src/backend/storage/lmgr/lock.c
@@ -1354,6 +1354,17 @@ LockCheckConflicts(LockMethod lockMethodTable,
 	}
 
 	/*
+	 * If relation lock for extend, it's a conflict even in
+	 * group locking.
+	 */
+	if ((lock->tag).locktag_type == LOCKTAG_RELATION_EXTEND)
+	{
+		PROCLOCK_PRINT("LockCheckConflicts: conflicting (group)",
+					   proclock);
+		return STATUS_FOUND;
+	}
+
+	/*
 	 * Locks held in conflicting modes by members of our own lock group are
 	 * not real conflicts; we can subtract those out and see if we still have
 	 * a conflict.  This is O(N) in the number of processes holding or