--- a/src/plugins/platforms/windows/qwindowsscreen.cpp	2020-08-06 14:54:16.467041500 +0200
+++ b/src/plugins/platforms/windows/qwindowsscreen.cpp1	2020-08-06 14:46:46.190897000 +0200
@@ -572,7 +572,8 @@
         }     // for existing screens
     }     // not lock screen
     if (primaryScreenChanged)
-        QWindowsTheme::instance()->refreshFonts();
+        if (QWindowsTheme *t = QWindowsTheme::instance())
+            t->refreshFonts();
     return true;
 }