diff --git a/source/Platform/Unix/Xlib.cpp b/source/Platform/Unix/Xlib.cpp
index bde34f8..41559e8 100644
--- a/source/Platform/Unix/Xlib.cpp
+++ b/source/Platform/Unix/Xlib.cpp
@@ -16,6 +16,7 @@ void init()
 
 void shutdown()
 {
+	assert(_priv::display != NULL);
 	XCloseDisplay(_priv::display);
 	_priv::display = NULL;
 }