Index: asterisk-svn/asterisk/channels/chan_sip.c
===================================================================
--- asterisk-svn/asterisk/channels/chan_sip.c	(Revision 153040)
+++ asterisk-svn/asterisk/channels/chan_sip.c	(Arbeitskopie)
@@ -18121,7 +18121,9 @@
 			sip_pvt_unlock(p);
 			if (p->refer->refer_call) {
 				sip_pvt_unlock(p->refer->refer_call);
-				ast_channel_unlock(p->refer->refer_call->owner);
+				if(p->refer->refer_call->owner) {
+					ast_channel_unlock(p->refer->refer_call->owner);
+				}
 			}
 			p->invitestate = INV_COMPLETED;
 			return -1;