diff --git a/proxy.go b/proxy.go
index ab0bf59..d18831d 100644
--- a/proxy.go
+++ b/proxy.go
@@ -84,7 +84,7 @@ func (rp *ReverseProxy) reverseProxyHandler(rw http.ResponseWriter, req *http.Re
 func parse_url(host_url string) *url.URL {
 	h_url, err := url.Parse(host_url)
 	if err != nil {
-		log.Fatal("[sidoxy] Invalid server URL: %v", host_url)
+		log.Fatal("[sidoxy] Invalid server URL: " + host_url)
 	}
 	return h_url
 }