diff --git a/winnativeeventfilter.cpp b/winnativeeventfilter.cpp
index e1b65f1..d8bf62c 100644
--- a/winnativeeventfilter.cpp
+++ b/winnativeeventfilter.cpp
@@ -32,7 +32,6 @@
 #endif
 #include <QLibrary>
 #include <QOperatingSystemVersion>
-#include <QTimer>
 #include <cmath>
 #include <windowsx.h>
 
@@ -215,7 +214,7 @@ QVector<HWND> m_framelessWindows;
 
 WinNativeEventFilter::WinNativeEventFilter() { initWin32Api(); }
 
-WinNativeEventFilter::~WinNativeEventFilter() = default;
+WinNativeEventFilter::~WinNativeEventFilter() { removeUserData(); };
 
 void WinNativeEventFilter::install() {
     if (m_instance.isNull()) {
@@ -494,7 +493,7 @@ bool WinNativeEventFilter::nativeEventFilter(const QByteArray &eventType,
             const auto isInSpecificAreas = [](int x, int y,
                                               const QVector<QRect> &areas,
                                               qreal dpr) -> bool {
-                for (auto &&area : qAsConst(areas)) {
+                for (auto &&area : std::as_const(areas)) {
                     if (!area.isValid()) {
                         continue;
                     }
@@ -914,3 +913,15 @@ qreal WinNativeEventFilter::getPreferedNumber(qreal num) {
 #endif
     return result;
 }
+
+void WinNativeEventFilter::removeUserData() {
+    // TODO: all top level windows of QGuiApplication.
+    if (!m_framelessWindows.isEmpty()) {
+        for (auto &&window : std::as_const(m_framelessWindows)) {
+            const auto userData = reinterpret_cast<WINDOW *>(m_lpGetWindowLongPtrW(window, GWLP_USERDATA));
+            if (userData) {
+                delete userData;
+            }
+        }
+    }
+}
diff --git a/winnativeeventfilter.h b/winnativeeventfilter.h
index 79ed7fd..8d1724e 100644
--- a/winnativeeventfilter.h
+++ b/winnativeeventfilter.h
@@ -54,6 +54,9 @@ public:
     ~WinNativeEventFilter() override;
 
     // Make all top level windows become frameless, unconditionally.
+    // Use setFramelessWindows or addFramelessWindow if possible,
+    // because this method will cause strange behavior, currently
+    // don't know why.
     static void install();
     // Make all top level windows back to normal.
     static void uninstall();
@@ -107,4 +110,5 @@ private:
     static UINT getDotsPerInchForWindow(HWND handle);
     static qreal getDevicePixelRatioForWindow(HWND handle);
     static int getSystemMetricsForWindow(HWND handle, int index);
+    void removeUserData();
 };