diff --git a/commit.c b/commit.c
index 718e568855..a92958cfac 100644
--- a/commit.c
+++ b/commit.c
@@ -760,7 +760,7 @@ static void fill_person(struct interp *table, const char *msg, int len)
 	if (msg + start == ep)
 		return;
 
-	table[5].value = xstrndup(msg + start, ep - msg + start);
+	table[5].value = xstrndup(msg + start, ep - (msg + start));
 
 	/* parse tz */
 	for (start = ep - msg + 1; start < len && isspace(msg[start]); start++)