diff --git a/http.c b/http.c
index 2a21ccbb7..105dc9384 100644
--- a/http.c
+++ b/http.c
@@ -583,7 +583,7 @@ static char *quote_ref_url(const char *base, const char *ref)
 	int len, baselen, ch;
 
 	baselen = strlen(base);
-	len = baselen + 7; /* "/refs/" + NUL */
+	len = baselen + 2; /* '/' after base and terminating NUL */
 	for (cp = ref; (ch = *cp) != 0; cp++, len++)
 		if (needs_quote(ch))
 			len += 2; /* extra two hex plus replacement % */