diff --git a/contrib/pageinspect/rawpage.c b/contrib/pageinspect/rawpage.c
index 2607576c378..1548dc2e257 100644
--- a/contrib/pageinspect/rawpage.c
+++ b/contrib/pageinspect/rawpage.c
@@ -135,9 +135,11 @@ get_raw_page_internal(text *relname, ForkNumber forknum, BlockNumber blkno)
 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 				 errmsg("cannot access temporary tables of other sessions")));
 
-	if (blkno >= RelationGetNumberOfBlocks(rel))
-		elog(ERROR, "block number %u is out of range for relation \"%s\"",
-			 blkno, RelationGetRelationName(rel));
+	if (blkno >= RelationGetNumberOfBlocksInFork(rel, forknum))
+		ereport(ERROR,
+				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+				 errmsg("block number %u is out of range for relation \"%s\"",
+						blkno, RelationGetRelationName(rel))));
 
 	/* Initialize buffer to copy to */
 	raw_page = (bytea *) palloc(BLCKSZ + VARHDRSZ);
diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index 58b64f6570d..aeb814e9efc 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -1926,8 +1926,8 @@ FlushBuffer(volatile BufferDesc *buf, SMgrRelation reln)
 }
 
 /*
- * RelationGetNumberOfBlocks
- *		Determines the current number of pages in the relation.
+ * RelationGetNumberOfBlocksInFork
+ *		Determines the current number of pages in the specified relation fork.
  */
 BlockNumber
 RelationGetNumberOfBlocksInFork(Relation relation, ForkNumber forkNum)