diff --git a/gemini/client.go b/gemini/client.go
index 05ab8cd..0e8dd07 100644
--- a/gemini/client.go
+++ b/gemini/client.go
@@ -38,7 +38,7 @@ func (client Client) RoundTrip(request *Request) (*Response, error) {
 
 	host := request.Host
 	if _, port, _ := net.SplitHostPort(host); port == "" {
-		host += ":1965"
+		host = net.JoinHostPort(host, "1965")
 	}
 
 	conn, err := tls.Dial("tcp", host, client.tlsConf)