Index: channels/chan_sip.c
===================================================================
--- channels/chan_sip.c	(revision 872)
+++ channels/chan_sip.c	(working copy)
@@ -7830,7 +7830,7 @@
  		/* If the registration username contains '@', then the domain should be used as
  		   the equivalent of "fromdomain" for the registration */
  		if (ast_strlen_zero(p->fromdomain)) {
- 			ast_string_field_set(p, fromdomain, ++fromdomain);
+ 			ast_string_field_set(p, fromdomain, fromdomain+1);
  		}
 	} else {
 		snprintf(from, sizeof(from), "<sip:%s@%s>;tag=%s", ast_uri_encode( r->username, tmp, sizeof(tmp), 0), p->tohost, p->tag);