diff --git a/src/corelib/itemmodels/qtransposeproxymodel_p.h b/src/corelib/itemmodels/qtransposeproxymodel_p.h
index 240fc4ccaee..fb5ce5c1179 100644
--- a/src/corelib/itemmodels/qtransposeproxymodel_p.h
+++ b/src/corelib/itemmodels/qtransposeproxymodel_p.h
@@ -40,6 +40,17 @@
 #ifndef QTRANSPOSEPROXYMODEL_P_H
 #define QTRANSPOSEPROXYMODEL_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 "qtransposeproxymodel.h"
 #include <private/qabstractproxymodel_p.h>