diff --git a/src/main.cpp b/src/main.cpp
index 35e7a2d2..3dd9ce1f 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -244,17 +244,13 @@ int main(int argc, char *argv[])
     font.setFamily("微软雅黑");
     _qApp.setFont(font);
 #endif
-    QStringList themes = QStyleFactory::keys();
-
-    if (themes.contains(QSTRING(confObject.UISettings.theme))) {
-        _qApp.setStyle(QSTRING(confObject.UISettings.theme));
-        LOG(MODULE_INIT " " MODULE_UI, "Setting Qv2ray UI themes.")
-    }
-
 #if QV2RAY_USE_BUILTIN_DARKTHEME
+    LOG(MODULE_UI, "Using built-in theme.")
 
     if (confObject.UISettings.useDarkTheme) {
+        LOG(MODULE_UI, " --> Using built-in dark theme.")
         // From https://forum.qt.io/topic/101391/windows-10-dark-theme/4
+        _qApp.setStyle("Fusion");
         QPalette darkPalette;
         QColor darkColor = QColor(45, 45, 45);
         QColor disabledColor = QColor(127, 127, 127);
@@ -280,6 +276,14 @@ int main(int argc, char *argv[])
         qApp->setStyleSheet("QToolTip { color: #ffffff; background-color: #2a82da; border: 1px solid white; }");
     }
 
+#else
+    QStringList themes = QStyleFactory::keys();
+
+    if (themes.contains(QSTRING(confObject.UISettings.theme))) {
+        _qApp.setStyle(QSTRING(confObject.UISettings.theme));
+        LOG(MODULE_INIT " " MODULE_UI, "Setting Qv2ray UI themes.")
+    }
+
 #endif
 
     try {
diff --git a/src/ui/w_PrefrencesWindow.cpp b/src/ui/w_PrefrencesWindow.cpp
index 333d132a..745dd3f8 100644
--- a/src/ui/w_PrefrencesWindow.cpp
+++ b/src/ui/w_PrefrencesWindow.cpp
@@ -33,6 +33,10 @@ PrefrencesWindow::PrefrencesWindow(QWidget *parent) : QDialog(parent),
     //
     themeCombo->setCurrentText(QSTRING(CurrentConfig.UISettings.theme));
     darkChartThemeCB->setChecked(CurrentConfig.UISettings.useDarkTheme);
+#if QV2RAY_USE_BUILTIN_DARKTHEME
+    // If we use built in theme, it should always be fusion.
+    themeCombo->setEnabled(!CurrentConfig.UISettings.useDarkTheme);
+#endif
     languageComboBox->setCurrentText(QSTRING(CurrentConfig.UISettings.language));
     logLevelComboBox->setCurrentIndex(CurrentConfig.logLevel);
     tProxyCheckBox->setChecked(CurrentConfig.tProxySupport);
@@ -712,4 +716,13 @@ void PrefrencesWindow::on_darkChartThemeCB_stateChanged(int arg1)
 {
     LOADINGCHECK
     CurrentConfig.UISettings.useDarkTheme = arg1 == Qt::Checked;
+#if QV2RAY_USE_BUILTIN_DARKTHEME
+    themeCombo->setEnabled(arg1 != Qt::Checked);
+
+    if (arg1 == Qt::Checked) {
+        themeCombo->setCurrentIndex(QStyleFactory::keys().indexOf("Fusion"));
+        CurrentConfig.UISettings.theme = "Fusion";
+    }
+
+#endif
 }