diff --git a/src/gtk/app.cpp b/src/gtk/app.cpp
index ec0827f78f..c9657f804b 100644
--- a/src/gtk/app.cpp
+++ b/src/gtk/app.cpp
@@ -428,7 +428,9 @@ void wxApp::CleanUp()
         g_source_remove(m_idleSourceId);
 
     // release reference acquired by Initialize()
-    g_type_class_unref(g_type_class_peek(GTK_TYPE_WIDGET));
+    gpointer gt = g_type_class_peek(GTK_TYPE_WIDGET);
+    if (gt != NULL)
+        g_type_class_unref(gt);
 
     gdk_threads_leave();