2 files changed, 15 insertions, 1 deletions
diff --git a/src/plugins/platforms/windows/qwindowscontext.cpp b/src/plugins/platforms/windows/qwindowscontext.cpp
index 6462cb8d3e..a74a7efb41 100644
--- a/src/plugins/platforms/windows/qwindowscontext.cpp
+++ b/src/plugins/platforms/windows/qwindowscontext.cpp
@@ -412,9 +412,17 @@ QString QWindowsContext::registerWindowClass(const QWindow *w, bool isGL)
         && (type == Qt::Popup || w->property("_q_windowsDropShadow").toBool())) {
         style |= CS_DROPSHADOW;
     }
-    if (type == Qt::Tool || type == Qt::ToolTip || type == Qt::Popup) {
+    switch (type) {
+    case Qt::Tool:
+    case Qt::ToolTip:
+    case Qt::Popup:
         style |= CS_SAVEBITS; // Save/restore background
         icon = false;
+        break;
+    case Qt::Dialog:
+        if (!(flags & Qt::WindowSystemMenuHint))
+            icon = false; // QTBUG-2027, dialogs without system menu.
+        break;
     }
     // Create a unique name for the flag combination
     QString cname = QStringLiteral("Qt5QWindow");
diff --git a/src/plugins/platforms/windows/qwindowswindow.cpp b/src/plugins/platforms/windows/qwindowswindow.cpp
index 3cf9481c17..274366d4fe 100644
--- a/src/plugins/platforms/windows/qwindowswindow.cpp
+++ b/src/plugins/platforms/windows/qwindowswindow.cpp
@@ -110,6 +110,8 @@ static QByteArray debugWinExStyle(DWORD exStyle)
         rc += " WS_EX_CONTEXTHELP";
     if (exStyle & WS_EX_LAYERED)
         rc += " WS_EX_LAYERED";
+    if (exStyle & WS_EX_DLGMODALFRAME)
+        rc += " WS_EX_DLGMODALFRAME";
     return rc;
 }
 
@@ -513,6 +515,10 @@ void WindowCreationData::fromWindow(const QWindow *w, const Qt::WindowFlags flag
                 }
                 if (flags & Qt::WindowSystemMenuHint)
                     style |= WS_SYSMENU;
+                else if (dialog) {
+                    style |= WS_SYSMENU | WS_BORDER; // QTBUG-2027, dialogs without system menu.
+                    exStyle |= WS_EX_DLGMODALFRAME;
+                }
                 if (flags & Qt::WindowMinimizeButtonHint)
                     style |= WS_MINIMIZEBOX;
                 if (shouldShowMaximizeButton(w, flags))