diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
index 4db3f2507f..1e2536c70e 100644
--- a/src/backend/access/heap/heapam.c
+++ b/src/backend/access/heap/heapam.c
@@ -7084,10 +7084,10 @@ heap_compute_xid_horizon_for_tuples(Relation rel,
 			xid_horizon_prefetch_buffer(rel, &prefetch_state, 1);
 #endif
 
+			LockBuffer(buf, BUFFER_LOCK_SHARE);
+
 			page = BufferGetPage(buf);
 			maxoff = PageGetMaxOffsetNumber(page);
-
-			LockBuffer(buf, BUFFER_LOCK_SHARE);
 		}
 
 		/*