diff --git a/lib/if2ip.c b/lib/if2ip.c
index 6fc09ec63..15ea9521e 100644
--- a/lib/if2ip.c
+++ b/lib/if2ip.c
@@ -191,7 +191,7 @@ bool Curl_if_is_interface_name(const char *interf)
   /* This is here just to support the old interfaces */
   char buf[256];
 
-  return (Curl_if2ip(AF_INET, 0, interf, buf, sizeof(buf)) ==
+  return (Curl_if2ip(AF_INET, 0 /* unused */, 0, interf, buf, sizeof(buf)) ==
           IF2IP_NOT_FOUND) ? FALSE : TRUE;
 }