diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index 9cc2470de87..0e4a8ac800a 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -4020,8 +4020,8 @@ local_buffer_write_error_callback(void *arg)
 static int
 rnode_comparator(const void *p1, const void *p2)
 {
-	RelFileNode n1 = *(RelFileNode *) p1;
-	RelFileNode n2 = *(RelFileNode *) p2;
+	RelFileNode n1 = *(const RelFileNode *) p1;
+	RelFileNode n2 = *(const RelFileNode *) p2;
 
 	if (n1.relNode < n2.relNode)
 		return -1;
@@ -4130,8 +4130,8 @@ buffertag_comparator(const void *a, const void *b)
 static int
 ckpt_buforder_comparator(const void *pa, const void *pb)
 {
-	const CkptSortItem *a = (CkptSortItem *) pa;
-	const CkptSortItem *b = (CkptSortItem *) pb;
+	const CkptSortItem *a = (const CkptSortItem *) pa;
+	const CkptSortItem *b = (const CkptSortItem *) pb;
 
 	/* compare tablespace */
 	if (a->tsId < b->tsId)
@@ -4151,8 +4151,10 @@ ckpt_buforder_comparator(const void *pa, const void *pb)
 	/* compare block number */
 	else if (a->blockNum < b->blockNum)
 		return -1;
-	else	/* should not be the same block ... */
+	else if (a->blockNum > b->blockNum)
 		return 1;
+	/* equal page IDs are unlikely, but not impossible */
+	return 0;
 }
 
 /*