Index: channels/chan_sip.c
===================================================================
--- channels/chan_sip.c	(revision 320498)
+++ channels/chan_sip.c	(working copy)
@@ -4225,6 +4225,11 @@
 	int res = -1;
 	struct sip_pvt *p = chan->tech_pvt;
 
+        if (!p) {
+        	ast_log(LOG_ERROR, "Attempt to Ref a null pointer.  sip private structure is gone!\n");
+        	return -1;
+        }
+
 	switch (option) {
 	case AST_OPTION_FORMAT_READ:
 		res = ast_rtp_instance_set_read_format(p->rtp, *(int *) data);