diff --git a/res/res_calendar.c b/res/res_calendar.c
index dfae4985a3..eebd7b480e 100644
--- a/res/res_calendar.c
+++ b/res/res_calendar.c
@@ -775,7 +775,10 @@ static void *do_notify(void *data)
 	datastore->inheritance = DATASTORE_INHERIT_FOREVER;
 
 	ao2_ref(event, +1);
+
+	ast_channel_lock(chan);
 	res = ast_channel_datastore_add(chan, datastore);
+	ast_channel_unlock(chan);
 
 	if (!(tmpstr = ast_str_create(32))) {
 		goto notify_cleanup;