diff --git a/src/widgets/dialogs/qcolordialog.cpp b/src/widgets/dialogs/qcolordialog.cpp
index c4cc21cbe5..8e699e87c5 100644
--- a/src/widgets/dialogs/qcolordialog.cpp
+++ b/src/widgets/dialogs/qcolordialog.cpp
@@ -1862,12 +1862,14 @@ void QColorDialogPrivate::retranslateStrings()
 
 bool QColorDialogPrivate::canBeNativeDialog() const
 {
-    Q_Q(const QColorDialog);
+    // Don't use Q_Q here! This function is called from ~QDialog,
+    // so Q_Q calling q_func() invokes undefined behavior (invalid cast in q_func()).
+    const QDialog * const q = static_cast<const QDialog*>(q_ptr);
     if (nativeDialogInUse)
         return true;
     if (q->testAttribute(Qt::WA_DontShowOnScreen))
         return false;
-    if (q->options() & QColorDialog::DontUseNativeDialog)
+    if (options->options() & QColorDialog::DontUseNativeDialog)
         return false;
 
     QLatin1String staticName(QColorDialog::staticMetaObject.className());
diff --git a/src/widgets/dialogs/qfiledialog.cpp b/src/widgets/dialogs/qfiledialog.cpp
index bc2de899f5..3aa9052917 100644
--- a/src/widgets/dialogs/qfiledialog.cpp
+++ b/src/widgets/dialogs/qfiledialog.cpp
@@ -695,12 +695,14 @@ void QFileDialogPrivate::emitFilesSelected(const QStringList &files)
 
 bool QFileDialogPrivate::canBeNativeDialog() const
 {
-    Q_Q(const QFileDialog);
+    // Don't use Q_Q here! This function is called from ~QDialog,
+    // so Q_Q calling q_func() invokes undefined behavior (invalid cast in q_func()).
+    const QDialog * const q = static_cast<const QDialog*>(q_ptr);
     if (nativeDialogInUse)
         return true;
     if (q->testAttribute(Qt::WA_DontShowOnScreen))
         return false;
-    if (q->options() & QFileDialog::DontUseNativeDialog)
+    if (options->options() & QFileDialog::DontUseNativeDialog)
         return false;
 
     QLatin1String staticName(QFileDialog::staticMetaObject.className());