diff --git a/src/backend/access/brin/brin_pageops.c b/src/backend/access/brin/brin_pageops.c
index 80f803e438e..b0f86f36639 100644
--- a/src/backend/access/brin/brin_pageops.c
+++ b/src/backend/access/brin/brin_pageops.c
@@ -113,9 +113,15 @@ brin_doupdate(Relation idxrel, BlockNumber pagesPerRange,
 
 	/*
 	 * Check that the old tuple wasn't updated concurrently: it might have
-	 * moved someplace else entirely ...
+	 * moved someplace else entirely, and for that matter the whole page
+	 * might've become a revmap page.  Note that in the first two cases
+	 * checked here, the "oldlp" we just calculated is garbage; but
+	 * PageGetItemId() is simple enough that it was safe to do that
+	 * calculation anyway.
 	 */
-	if (!ItemIdIsNormal(oldlp))
+	if (!BRIN_IS_REGULAR_PAGE(oldpage) ||
+		oldoff > PageGetMaxOffsetNumber(oldpage) ||
+		!ItemIdIsNormal(oldlp))
 	{
 		LockBuffer(oldbuf, BUFFER_LOCK_UNLOCK);