diff --git a/src/gui/kernel/qplatformwindow.h b/src/gui/kernel/qplatformwindow.h
index 76624835a7..5ec2ecb2e0 100644
--- a/src/gui/kernel/qplatformwindow.h
+++ b/src/gui/kernel/qplatformwindow.h
@@ -170,6 +170,20 @@ protected:
     QScopedPointer<QPlatformWindowPrivate> d_ptr;
 };
 
+// ----------------- QPlatformInterface -----------------
+
+namespace QPlatformInterface::Private {
+
+#if defined(Q_OS_MACOS)
+struct Q_GUI_EXPORT QCocoaWindow
+{
+    QT_DECLARE_PLATFORM_INTERFACE(QCocoaWindow)
+    virtual void setContentBorderEnabled(bool enable) = 0;
+};
+#endif
+
+} // QPlatformInterface::Private
+
 QT_END_NAMESPACE
 
 #endif //QPLATFORMWINDOW_H
diff --git a/src/gui/platform/macos/qcocoaplatforminterface.mm b/src/gui/platform/macos/qcocoaplatforminterface.mm
index 2fc9228ab1..a14335e077 100644
--- a/src/gui/platform/macos/qcocoaplatforminterface.mm
+++ b/src/gui/platform/macos/qcocoaplatforminterface.mm
@@ -41,6 +41,7 @@
 #include <QtGui/private/qguiapplication_p.h>
 #include <qpa/qplatformopenglcontext.h>
 #include <qpa/qplatformintegration.h>
+#include <qpa/qplatformwindow.h>
 
 #include <AppKit/AppKit.h>
 
@@ -52,6 +53,7 @@ using namespace QPlatformInterface::Private;
 
 QT_DEFINE_PLATFORM_INTERFACE(QCocoaGLContext, QOpenGLContext);
 QT_DEFINE_PRIVATE_PLATFORM_INTERFACE(QCocoaGLIntegration);
+QT_DEFINE_PRIVATE_PLATFORM_INTERFACE(QCocoaWindow);
 
 QOpenGLContext *QPlatformInterface::QCocoaGLContext::fromNative(NSOpenGLContext *nativeContext, QOpenGLContext *shareContext)
 {
diff --git a/src/plugins/platforms/cocoa/qcocoanativeinterface.h b/src/plugins/platforms/cocoa/qcocoanativeinterface.h
index 7d4c5884b3..4f82faf39b 100644
--- a/src/plugins/platforms/cocoa/qcocoanativeinterface.h
+++ b/src/plugins/platforms/cocoa/qcocoanativeinterface.h
@@ -105,9 +105,6 @@ private:
     // deregisters.
     static void registerTouchWindow(QWindow *window,  bool enable);
 
-    // Enable the unified title and toolbar area for a window.
-    static void setContentBorderEnabled(QWindow *window, bool enable);
-
     // Set the size of the unified title and toolbar area.
     static void setContentBorderThickness(QWindow *window, int topThickness, int bottomThickness);
 
diff --git a/src/plugins/platforms/cocoa/qcocoanativeinterface.mm b/src/plugins/platforms/cocoa/qcocoanativeinterface.mm
index 426e413a86..77187f2d20 100644
--- a/src/plugins/platforms/cocoa/qcocoanativeinterface.mm
+++ b/src/plugins/platforms/cocoa/qcocoanativeinterface.mm
@@ -118,8 +118,6 @@ QPlatformNativeInterface::NativeResourceForIntegrationFunction QCocoaNativeInter
         return NativeResourceForIntegrationFunction(QCocoaNativeInterface::registerContentBorderArea);
     if (resource.toLower() == "setcontentborderareaenabled")
         return NativeResourceForIntegrationFunction(QCocoaNativeInterface::setContentBorderAreaEnabled);
-    if (resource.toLower() == "setcontentborderenabled")
-        return NativeResourceForIntegrationFunction(QCocoaNativeInterface::setContentBorderEnabled);
     if (resource.toLower() == "setnstoolbar")
         return NativeResourceForIntegrationFunction(QCocoaNativeInterface::setNSToolbar);
     if (resource.toLower() == "testcontentborderposition")
@@ -260,16 +258,6 @@ void QCocoaNativeInterface::setContentBorderAreaEnabled(QWindow *window, quintpt
         cocoaWindow->setContentBorderAreaEnabled(identifier, enable);
 }
 
-void QCocoaNativeInterface::setContentBorderEnabled(QWindow *window, bool enable)
-{
-    if (!window)
-        return;
-
-    QCocoaWindow *cocoaWindow = static_cast<QCocoaWindow *>(window->handle());
-    if (cocoaWindow)
-        cocoaWindow->setContentBorderEnabled(enable);
-}
-
 void QCocoaNativeInterface::setNSToolbar(QWindow *window, void *nsToolbar)
 {
     QCocoaIntegration::instance()->setToolbar(window, static_cast<NSToolbar *>(nsToolbar));
diff --git a/src/plugins/platforms/cocoa/qcocoawindow.h b/src/plugins/platforms/cocoa/qcocoawindow.h
index e4debd669d..0c607320f8 100644
--- a/src/plugins/platforms/cocoa/qcocoawindow.h
+++ b/src/plugins/platforms/cocoa/qcocoawindow.h
@@ -98,7 +98,8 @@ class QDebug;
 
 class QCocoaMenuBar;
 
-class QCocoaWindow : public QObject, public QPlatformWindow
+class QCocoaWindow : public QObject, public QPlatformWindow,
+    public QPlatformInterface::Private::QCocoaWindow
 {
     Q_OBJECT
 public:
@@ -192,7 +193,7 @@ public:
     void setContentBorderThickness(int topThickness, int bottomThickness);
     void registerContentBorderArea(quintptr identifier, int upper, int lower);
     void setContentBorderAreaEnabled(quintptr identifier, bool enable);
-    void setContentBorderEnabled(bool enable);
+    void setContentBorderEnabled(bool enable) override;
     bool testContentBorderAreaPosition(int position) const;
     void applyContentBorderThickness(NSWindow *window = nullptr);
     void updateNSToolbar();
diff --git a/src/widgets/widgets/qmainwindow.cpp b/src/widgets/widgets/qmainwindow.cpp
index 7fabb4ae7c..9379fb04ef 100644
--- a/src/widgets/widgets/qmainwindow.cpp
+++ b/src/widgets/widgets/qmainwindow.cpp
@@ -67,9 +67,7 @@
 #include "qtoolbar_p.h"
 #endif
 #include "qwidgetanimator_p.h"
-#ifdef Q_OS_MACOS
-#include <qpa/qplatformnativeinterface.h>
-#endif
+#include <QtGui/qpa/qplatformwindow.h>
 
 QT_BEGIN_NAMESPACE
 
@@ -1351,28 +1349,23 @@ bool QMainWindow::event(QEvent *event)
 
     \since 5.2
 */
-void QMainWindow::setUnifiedTitleAndToolBarOnMac(bool set)
+void QMainWindow::setUnifiedTitleAndToolBarOnMac(bool enabled)
 {
 #ifdef Q_OS_MACOS
+    if (!isWindow())
+        return;
+
     Q_D(QMainWindow);
-    if (isWindow()) {
-        d->useUnifiedToolBar = set;
-        createWinId();
+    d->useUnifiedToolBar = enabled;
+    createWinId();
 
-        QPlatformNativeInterface *nativeInterface = QGuiApplication::platformNativeInterface();
-        if (!nativeInterface)
-            return; // Not Cocoa platform plugin.
-        QPlatformNativeInterface::NativeResourceForIntegrationFunction function =
-            nativeInterface->nativeResourceFunctionForIntegration("setContentBorderEnabled");
-        if (!function)
-            return; // Not Cocoa platform plugin.
+    using namespace QPlatformInterface::Private;
+    if (auto *platformWindow = dynamic_cast<QCocoaWindow*>(window()->windowHandle()->handle()))
+        platformWindow->setContentBorderEnabled(enabled);
 
-        typedef void (*SetContentBorderEnabledFunction)(QWindow *window, bool enable);
-        (reinterpret_cast<SetContentBorderEnabledFunction>(function))(window()->windowHandle(), set);
-        update();
-    }
+    update();
 #else
-    Q_UNUSED(set)
+    Q_UNUSED(enabled)
 #endif
 }