diff --git a/qt5/style/qtcurve.cpp b/qt5/style/qtcurve.cpp
--- a/qt5/style/qtcurve.cpp
+++ b/qt5/style/qtcurve.cpp
@@ -755,7 +755,7 @@
                    this, SLOT(compositingToggled()));
 #endif
 
-    QString arg0 = qApp? qApp->arguments()[0] : QString();
+    QString arg0 = (qApp && qApp->arguments().size()) ? qApp->arguments()[0] : QString();
     if (!qApp || (arg0 != "kwin" && arg0 != "kwin_x11" && arg0 != "kwin_wayland")) {
         bus.disconnect("org.kde.kwin", "/QtCurve", "org.kde.QtCurve",
                     "borderSizesChanged", this, SLOT(borderSizesChanged()));