diff --git a/src/backend/storage/file/buffile.c b/src/backend/storage/file/buffile.c
index dd687dfe71..d3722616bb 100644
--- a/src/backend/storage/file/buffile.c
+++ b/src/backend/storage/file/buffile.c
@@ -768,17 +768,17 @@ BufFileTellBlock(BufFile *file)
  * Counts any holes left behind by BufFileAppend as part of the size.
  * Returns -1 on error.
  */
-off_t
+int64
 BufFileSize(BufFile *file)
 {
-	off_t		lastFileSize;
+	int64		lastFileSize;
 
 	/* Get the size of the last physical file. */
 	lastFileSize = FileSize(file->files[file->numFiles - 1]);
 	if (lastFileSize < 0)
 		return -1;
 
-	return ((file->numFiles - 1) * (off_t) MAX_PHYSICAL_FILESIZE) +
+	return ((file->numFiles - 1) * (int64) MAX_PHYSICAL_FILESIZE) +
 		lastFileSize;
 }
 
diff --git a/src/backend/utils/sort/logtape.c b/src/backend/utils/sort/logtape.c
index 50a150b713..269523d5f6 100644
--- a/src/backend/utils/sort/logtape.c
+++ b/src/backend/utils/sort/logtape.c
@@ -426,7 +426,7 @@ ltsConcatWorkerTapes(LogicalTapeSet *lts, TapeShare *shared,
 	{
 		char		filename[MAXPGPATH];
 		BufFile    *file;
-		off_t		filesize;
+		int64		filesize;
 
 		lt = &lts->tapes[i];
 
diff --git a/src/include/storage/buffile.h b/src/include/storage/buffile.h
index a6cdeb451c..a4043bd69d 100644
--- a/src/include/storage/buffile.h
+++ b/src/include/storage/buffile.h
@@ -43,7 +43,7 @@ extern size_t BufFileWrite(BufFile *file, void *ptr, size_t size);
 extern int	BufFileSeek(BufFile *file, int fileno, off_t offset, int whence);
 extern void BufFileTell(BufFile *file, int *fileno, off_t *offset);
 extern int	BufFileSeekBlock(BufFile *file, long blknum);
-extern off_t BufFileSize(BufFile *file);
+extern int64 BufFileSize(BufFile *file);
 extern long BufFileAppend(BufFile *target, BufFile *source);
 
 extern BufFile *BufFileCreateShared(SharedFileSet *fileset, const char *name);