diff --git a/framelesshelper_win32.cpp b/framelesshelper_win32.cpp
index 6629e26..fc13efb 100644
--- a/framelesshelper_win32.cpp
+++ b/framelesshelper_win32.cpp
@@ -247,7 +247,7 @@ bool FramelessHelperWin::nativeEventFilter(const QByteArray &eventType, void *me
                                  ? reinterpret_cast<LPRECT>(msg->lParam)
                                  : &(reinterpret_cast<LPNCCALCSIZE_PARAMS>(msg->lParam))->rgrc[0]);
         const bool max = IsMaximized(msg->hwnd);
-        const bool full = window->windowState() == Qt::WindowFullScreen;
+        const bool full = Utilities::isFullScreen(reinterpret_cast<WId>(msg->hwnd));
         // We don't need this correction when we're fullscreen. We will
         // have the WS_POPUP size, so we don't have to worry about
         // borders, and the default frame will be fine.
@@ -574,12 +574,12 @@ bool FramelessHelperWin::nativeEventFilter(const QByteArray &eventType, void *me
         const int titleBarHeight = Utilities::getSystemMetric(window, SystemMetric::TitleBarHeight, true);
         bool isTitleBar = false;
         const bool max = IsMaximized(msg->hwnd);
-        if (max || (window->windowState() == Qt::WindowFullScreen)) {
+        if (max || Utilities::isFullScreen(reinterpret_cast<WId>(msg->hwnd))) {
             isTitleBar = (localMouse.y() >= 0) && (localMouse.y() <= titleBarHeight)
                     && (localMouse.x() >= 0) && (localMouse.x() <= windowWidth)
                     && !Utilities::isHitTestVisible(window);
         }
-        if (window->windowState() == Qt::WindowNoState) {
+        if (Utilities::isWindowNoState(reinterpret_cast<WId>(msg->hwnd))) {
             isTitleBar = (localMouse.y() > resizeBorderThickness) && (localMouse.y() <= titleBarHeight)
                     && (localMouse.x() > resizeBorderThickness) && (localMouse.x() < (windowWidth - resizeBorderThickness))
                     && !Utilities::isHitTestVisible(window);
diff --git a/utilities.h b/utilities.h
index 82e2326..5cf4ed8 100644
--- a/utilities.h
+++ b/utilities.h
@@ -55,6 +55,8 @@ FRAMELESSHELPER_API void triggerFrameChange(const WId winId);
 FRAMELESSHELPER_API void updateFrameMargins(const WId winId, const bool reset);
 FRAMELESSHELPER_API void updateQtFrameMargins(QWindow *window, const bool enable);
 [[nodiscard]] FRAMELESSHELPER_API QString getSystemErrorMessage(const QString &function);
+[[nodiscard]] FRAMELESSHELPER_API bool isFullScreen(const WId winId);
+[[nodiscard]] FRAMELESSHELPER_API bool isWindowNoState(const WId winId);
 #endif
 
 }
diff --git a/utilities_win32.cpp b/utilities_win32.cpp
index 0076a6b..502443b 100644
--- a/utilities_win32.cpp
+++ b/utilities_win32.cpp
@@ -547,4 +547,53 @@ bool Utilities::showSystemMenu(const WId winId, const QPointF &pos)
     return true;
 }
 
+bool Utilities::isFullScreen(const WId winId)
+{
+    Q_ASSERT(winId);
+    if (!winId) {
+        return false;
+    }
+    const auto hwnd = reinterpret_cast<HWND>(winId);
+    RECT wndRect = {};
+    if (GetWindowRect(hwnd, &wndRect) == FALSE) {
+        qWarning() << getSystemErrorMessage(QStringLiteral("GetWindowRect"));
+        return false;
+    }
+    // According to Microsoft Docs, we should compare to primary
+    // screen's geometry.
+    const HMONITOR mon = MonitorFromWindow(hwnd, MONITOR_DEFAULTTOPRIMARY);
+    if (!mon) {
+        qWarning() << getSystemErrorMessage(QStringLiteral("MonitorFromWindow"));
+        return false;
+    }
+    MONITORINFO mi;
+    SecureZeroMemory(&mi, sizeof(mi));
+    mi.cbSize = sizeof(mi);
+    if (GetMonitorInfoW(mon, &mi) == FALSE) {
+        qWarning() << getSystemErrorMessage(QStringLiteral("GetMonitorInfoW"));
+        return false;
+    }
+    // Compare to the full area of the screen, not the work area.
+    const RECT scrRect = mi.rcMonitor;
+    return ((wndRect.left == scrRect.left) && (wndRect.top == scrRect.top)
+            && (wndRect.right == scrRect.right) && (wndRect.bottom == scrRect.bottom));
+}
+
+bool Utilities::isWindowNoState(const WId winId)
+{
+    Q_ASSERT(winId);
+    if (!winId) {
+        return false;
+    }
+    const auto hwnd = reinterpret_cast<HWND>(winId);
+    WINDOWPLACEMENT wp;
+    SecureZeroMemory(&wp, sizeof(wp));
+    wp.length = sizeof(wp);
+    if (GetWindowPlacement(hwnd, &wp) == FALSE) {
+        qWarning() << getSystemErrorMessage(QStringLiteral("GetWindowPlacement"));
+        return false;
+    }
+    return ((wp.showCmd == SW_NORMAL) || (wp.showCmd == SW_RESTORE));
+}
+
 FRAMELESSHELPER_END_NAMESPACE