diff --git a/src/gui/platform/darwin/qapplekeymapper_p.h b/src/gui/platform/darwin/qapplekeymapper_p.h
index d8ad6bd45ce..aed9907d922 100644
--- a/src/gui/platform/darwin/qapplekeymapper_p.h
+++ b/src/gui/platform/darwin/qapplekeymapper_p.h
@@ -40,6 +40,17 @@
 #ifndef QAPPLEKEYMAPPER_H
 #define QAPPLEKEYMAPPER_H
 
+//
+//  W A R N I N G
+//  -------------
+//
+// This file is not part of the Qt API.  It exists purely as an
+// implementation detail.  This header file may change from version to
+// version without notice, or even be removed.
+//
+// We mean it.
+//
+
 #ifdef Q_OS_MACOS
 #include <Carbon/Carbon.h>
 #endif