Index: channels/chan_sip.c
===================================================================
--- channels/chan_sip.c	(revision 321272)
+++ channels/chan_sip.c	(working copy)
@@ -18536,7 +18536,7 @@
 	struct sip_auth *auth = NULL;	/* Realm authentication */
 
 	if (!ast_strlen_zero(p->domain))
-		ast_copy_string(uri, p->domain, sizeof(uri));
+		snprintf(uri, sizeof(uri), "sip:%s", p->domain);
 	else if (!ast_strlen_zero(p->uri))
 		ast_copy_string(uri, p->uri, sizeof(uri));
 	else