diff --git a/lib/http.c b/lib/http.c
index 9820b8f62..b6c01395a 100644
--- a/lib/http.c
+++ b/lib/http.c
@@ -3063,6 +3063,8 @@ checkprotoprefix(struct SessionHandle *data, struct connectdata *conn,
 #ifndef CURL_DISABLE_RTSP
   if(conn->protocol & PROT_RTSP)
     return checkrtspprefix(data, s);
+#else
+  (void)conn;
 #endif /* CURL_DISABLE_RTSP */
 
   return checkhttpprefix(data, s);