diff -uNr asterisk-1.8.4.ORIG/channels/chan_sip.c asterisk-1.8.4/channels/chan_sip.c
--- asterisk-1.8.4.ORIG/channels/chan_sip.c	2011-05-13 11:39:08.916004752 +0100
+++ asterisk-1.8.4/channels/chan_sip.c	2011-05-13 11:40:56.435004807 +0100
@@ -2728,7 +2728,7 @@
 	ast_debug(2, "Shutting down thread for %s server\n", tcptls_session->ssl ? "SSL" : "TCP");
 
 cleanup:
-	if (!tcptls_session->client && !authenticated) {
+	if (tcptls_session && !tcptls_session->client && !authenticated) {
 		ast_atomic_fetchadd_int(&unauth_sessions, -1);
 	}