diff --git a/channels/chan_sip.c b/channels/chan_sip.c
index fc9937eaaf..ee68902b56 100644
--- a/channels/chan_sip.c
+++ b/channels/chan_sip.c
@@ -18460,7 +18460,7 @@ static int unload_module(void)
 	dialoglist_unlock();
 
 	ast_mutex_lock(&monlock);
-	if (monitor_thread && (monitor_thread != AST_PTHREADT_STOP)) {
+	if (monitor_thread && (monitor_thread != AST_PTHREADT_STOP) && (monitor_thread != AST_PTHREADT_NULL)) {
 		pthread_cancel(monitor_thread);
 		pthread_kill(monitor_thread, SIGURG);
 		pthread_join(monitor_thread, NULL);