diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 2f5d603066..a2ea03506a 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -1940,6 +1940,7 @@ AdvanceXLInsertBuffer(XLogRecPtr upto, bool opportunistic)
 		 * already written out.
 		 */
 		OldPageRqstPtr = XLogCtl->xlblocks[nextidx];
+		Assert(OldPageRqstPtr <= XLogCtl->InitializedUpTo);
 		if (LogwrtResult.Write < OldPageRqstPtr)
 		{
 			/*
@@ -1970,6 +1971,10 @@ AdvanceXLInsertBuffer(XLogRecPtr upto, bool opportunistic)
 				 */
 				LWLockRelease(WALBufMappingLock);
 
+				/* we should exit the loop before reaching a page beyond the
+				 * requested 'upto' position. */
+				Assert(OldPageRqstPtr <= upto || opportunistic);
+
 				WaitXLogInsertionsToFinish(OldPageRqstPtr);
 
 				LWLockAcquire(WALWriteLock, LW_EXCLUSIVE);