diff --git a/src/or/rendservice.c b/src/or/rendservice.c
index 4f7d7aa726..114a56b74e 100644
--- a/src/or/rendservice.c
+++ b/src/or/rendservice.c
@@ -1490,7 +1490,7 @@ rend_service_load_auth_keys(rend_service_t *s, const char *hfname)
   strmap_free(parsed_clients, rend_authorized_client_strmap_item_free);
 
   if (cfname) {
-    memwipe(cfname, 0, sizeof(cfname));
+    memwipe(cfname, 0, strlen(cfname));
     tor_free(cfname);
   }