diff --git a/Furious/Window/MainWindow.py b/Furious/Window/MainWindow.py
index ba5da0f..d781448 100644
--- a/Furious/Window/MainWindow.py
+++ b/Furious/Window/MainWindow.py
@@ -65,6 +65,8 @@ class MainWindow(AppQMainWindow):
         QtCore.QSize(1800, 960) if PLATFORM != 'Darwin' else DEFAULT_WINDOW_SIZE_DARWIN
     )
 
+    QT_FALLBACK_WINDOW_SIZE = QtCore.QSize(640, 480)
+
     def __init__(self, *args, **kwargs):
         """Create and register the built-in application pages."""
         super().__init__(*args, **kwargs)
@@ -251,7 +253,15 @@ class MainWindow(AppQMainWindow):
 
                 restored = False
 
-            if restored:
+            if (
+                restored
+                and PLATFORM == 'Darwin'
+                and self.size() == self.QT_FALLBACK_WINDOW_SIZE
+            ):
+                self._applyDefaultWindowSize(
+                    'saved macOS main-window geometry restored to the Qt fallback size'
+                )
+            elif restored:
                 logger.info(
                     f'restored main-window geometry: {self.geometry().getRect()}'
                 )
diff --git a/tests/test_main_window_geometry.py b/tests/test_main_window_geometry.py
index d08a42f..4623ffc 100644
--- a/tests/test_main_window_geometry.py
+++ b/tests/test_main_window_geometry.py
@@ -82,6 +82,7 @@ class _GeometryWindow(AppQMainWindow):
 
     DEFAULT_WINDOW_SIZE = QtCore.QSize(700, 500)
 
+    QT_FALLBACK_WINDOW_SIZE = MainWindow.QT_FALLBACK_WINDOW_SIZE
     _applyDefaultWindowSize = MainWindow._applyDefaultWindowSize
     _restoreLegacyWindowSize = MainWindow._restoreLegacyWindowSize
     _restoreMainWindowState = MainWindow._restoreMainWindowState
@@ -359,8 +360,8 @@ class MainWindowGeometryTest(unittest.TestCase):
                 window.close()
                 window.deleteLater()
 
-    def testValidIntentional640By480GeometryIsPreserved(self):
-        """Never reinterpret a successful small user geometry as Qt fallback."""
+    def testDarwinRestoredQtFallbackSizeUsesCanonicalDefault(self):
+        """Replace macOS Qt fallback dimensions with the product default."""
         with isolatedSettings():
             expected = QtCore.QRect(40, 50, 640, 480)
             AppSettings.set(
@@ -370,7 +371,31 @@ class MainWindowGeometryTest(unittest.TestCase):
 
             window = _GeometryWindow()
 
-            with patch('Furious.Qt.QtWidgets.moveToCenter') as moveToCenter:
+            with patch('Furious.Window.MainWindow.PLATFORM', 'Darwin'), patch(
+                'Furious.Qt.QtWidgets.moveToCenter'
+            ) as moveToCenter:
+                window.show()
+
+                self.assertEqual(window.size(), window.DEFAULT_WINDOW_SIZE)
+                moveToCenter.assert_not_called()
+
+            window.close()
+            window.deleteLater()
+
+    def testNonDarwinRestored640By480GeometryIsPreserved(self):
+        """Preserve a successful 640 by 480 restoration outside macOS."""
+        with isolatedSettings():
+            expected = QtCore.QRect(40, 50, 640, 480)
+            AppSettings.set(
+                'AppMainWindowGeometry',
+                self._saveGeometry(expected),
+            )
+
+            window = _GeometryWindow()
+
+            with patch('Furious.Window.MainWindow.PLATFORM', 'Windows'), patch(
+                'Furious.Qt.QtWidgets.moveToCenter'
+            ) as moveToCenter:
                 window.show()
 
                 self.assertEqual(window.size(), expected.size())