diff --git a/diff-process.c b/diff-process.c
index 121903a6c8..d28f9cf973 100644
--- a/diff-process.c
+++ b/diff-process.c
@@ -325,7 +325,7 @@ static int validate_external_hunks(const struct xdl_hunk *hunks, size_t nr,
  */
 static long blob_line_cap(struct repository *r, const struct object_id *oid)
 {
-	unsigned long size;
+	size_t size;
 	struct object_info oi = OBJECT_INFO_INIT;
 
 	oi.sizep = &size;