diff --git a/src/ui/LmsApplicationGroup.cpp b/src/ui/LmsApplicationGroup.cpp
index 8a742486..36e0647b 100644
--- a/src/ui/LmsApplicationGroup.cpp
+++ b/src/ui/LmsApplicationGroup.cpp
@@ -45,6 +45,8 @@ LmsApplicationGroup::join(LmsApplicationInfo info)
 void
 LmsApplicationGroup::leave()
 {
+	std::lock_guard<std::mutex> lock(_mutex);
+
 	_apps.erase(wApp->sessionId());
 }