diff --git a/pkgs/development/libraries/qtstyleplugin-kvantum/default.nix b/pkgs/development/libraries/qtstyleplugin-kvantum/default.nix
index fc9122f5cd72..61be4606df9d 100644
--- a/pkgs/development/libraries/qtstyleplugin-kvantum/default.nix
+++ b/pkgs/development/libraries/qtstyleplugin-kvantum/default.nix
@@ -8,7 +8,7 @@
   qtbase,
   qtsvg,
   qtx11extras ? null, # Qt 5 only
-  kwindowsystem,
+  kwindowsystem ? null, # Qt 6 only
   qtwayland,
   libx11,
   libxext,