diff --git a/contrib/pgstattuple/pgstatindex.c b/contrib/pgstattuple/pgstatindex.c
index 2982ceaf50..f1385ef0c8 100644
--- a/contrib/pgstattuple/pgstatindex.c
+++ b/contrib/pgstattuple/pgstatindex.c
@@ -63,14 +63,15 @@ extern Datum pg_relpages(PG_FUNCTION_ARGS);
 #define IS_INDEX(r) ((r)->rd_rel->relkind == 'i')
 #define IS_BTREE(r) ((r)->rd_rel->relam == BTREE_AM_OID)
 
-#define CHECK_PAGE_OFFSET_RANGE(page, offset) { \
-		if ( !(FirstOffsetNumber<=(offset) && \
-						(offset)<=PageGetMaxOffsetNumber(page)) ) \
-			 elog(ERROR, "Page offset number out of range."); }
+#define CHECK_PAGE_OFFSET_RANGE(pg, offnum) { \
+		if ( !(FirstOffsetNumber <= (offnum) && \
+						(offnum) <= PageGetMaxOffsetNumber(pg)) ) \
+			 elog(ERROR, "page offset number out of range"); }
 
+/* note: BlockNumber is unsigned, hence can't be negative */
 #define CHECK_RELATION_BLOCK_RANGE(rel, blkno) { \
-		if ( (blkno)<0 && RelationGetNumberOfBlocks((rel))<=(blkno) ) \
-			 elog(ERROR, "Block number out of range."); }
+		if ( RelationGetNumberOfBlocks(rel) <= (BlockNumber) (blkno) ) \
+			 elog(ERROR, "block number out of range"); }
 
 /* ------------------------------------------------
  * structure for single btree page statistics