diff --git a/xdiff/xtypes.h b/xdiff/xtypes.h
index f145abba3e..7a2d429ec5 100644
--- a/xdiff/xtypes.h
+++ b/xdiff/xtypes.h
@@ -47,7 +47,7 @@ typedef struct s_xrecord {
 typedef struct s_xdfile {
 	xrecord_t *recs;
 	long nrec;
-	long dstart, dend;
+	ptrdiff_t dstart, dend;
 	bool *changed;
 	long *rindex;
 	long nreff;