diff --git a/pkgs/desktops/plasma-5.5/kde-gtk-config/default.nix b/pkgs/desktops/plasma-5.5/kde-gtk-config/default.nix
index 6b41599994d..ab8867520b3 100644
--- a/pkgs/desktops/plasma-5.5/kde-gtk-config/default.nix
+++ b/pkgs/desktops/plasma-5.5/kde-gtk-config/default.nix
@@ -22,7 +22,7 @@ plasmaPackage {
   ];
   propagatedBuildInputs = [ ki18n kio ];
   cmakeFlags = [
-    "-DGTK2_GLIBCONFIG_INCLUDE_DIR=${glib}/lib/glib-2.0/include"
-    "-DGTK2_GDKCONFIG_INCLUDE_DIR=${gtk2}/lib/gtk-2.0/include"
+    "-DGTK2_GLIBCONFIG_INCLUDE_DIR=${glib.out}/lib/glib-2.0/include"
+    "-DGTK2_GDKCONFIG_INCLUDE_DIR=${gtk2.out}/lib/gtk-2.0/include"
   ];
 }