diff --git a/library/SIP_Templates.ttcn b/library/SIP_Templates.ttcn
index ffd6f2b..37dee4b 100644
--- a/library/SIP_Templates.ttcn
+++ b/library/SIP_Templates.ttcn
@@ -1388,7 +1388,7 @@
 }
 
 function f_sip_SipUrl_to_str(SipUrl uri) return charstring {
-	var charstring str := uri.scheme & f_sip_HostPort_to_str(uri.hostPort);
+	var charstring str := uri.scheme & ":" & f_sip_HostPort_to_str(uri.hostPort);
 	return str;
 }