diff --git a/src/corelib/global/qnamespace.h b/src/corelib/global/qnamespace.h
index e6caf798d8a..366cfb5ed9a 100644
--- a/src/corelib/global/qnamespace.h
+++ b/src/corelib/global/qnamespace.h
@@ -44,6 +44,10 @@
 
 #include <QtCore/qglobal.h>
 
+#if defined(__OBJC__) && !defined(__cplusplus)
+#  warning "File built in Objective-C mode (.m), but using Qt requires Objective-C++ (.mm)"
+#endif
+
 QT_BEGIN_NAMESPACE
 
 
diff --git a/src/corelib/kernel/qobjectdefs.h b/src/corelib/kernel/qobjectdefs.h
index c3141c1abb9..fe107f14253 100644
--- a/src/corelib/kernel/qobjectdefs.h
+++ b/src/corelib/kernel/qobjectdefs.h
@@ -42,6 +42,10 @@
 #ifndef QOBJECTDEFS_H
 #define QOBJECTDEFS_H
 
+#if defined(__OBJC__) && !defined(__cplusplus)
+#  warning "File built in Objective-C mode (.m), but using Qt requires Objective-C++ (.mm)"
+#endif
+
 #include <QtCore/qnamespace.h>
 
 #include <QtCore/qobjectdefs_impl.h>