diff --git a/src/gui/platform/windows/qwindowsmime_p.h b/src/gui/platform/windows/qwindowsmime_p.h
index e90f596d1d7..91b1d104b71 100644
--- a/src/gui/platform/windows/qwindowsmime_p.h
+++ b/src/gui/platform/windows/qwindowsmime_p.h
@@ -40,6 +40,17 @@
 #ifndef QWINDOWSMIME_P_H
 #define QWINDOWSMIME_P_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.
+//
+
 #include <QtCore/qt_windows.h>
 #include <QtCore/qvariant.h>