Index: channels/chan_sip.c
===================================================================
--- channels/chan_sip.c	(revision 81157)
+++ channels/chan_sip.c	(working copy)
@@ -10439,7 +10439,14 @@
 	/* Make formats okay */
 	chan2m->readformat = chan2->readformat;
 	chan2m->writeformat = chan2->writeformat;
+	while (ast_mutex_trylock(&chan2->lock)) {
+		struct sip_pvt *pvt = chan2->tech_pvt;
+		ast_mutex_unlock(&pvt->lock);
+		usleep(1);
+		ast_mutex_lock(&pvt->lock);
+	}
 	ast_channel_masquerade(chan2m, chan2);
+	ast_mutex_unlock(&chan2->lock);
 	/* Setup the extensions and such */
 	ast_copy_string(chan2m->context, chan2->context, sizeof(chan2m->context));
 	ast_copy_string(chan2m->exten, chan2->exten, sizeof(chan2m->exten));