diff --git a/kitty/window.py b/kitty/window.py
index 1dc86bfac..4c514f150 100644
--- a/kitty/window.py
+++ b/kitty/window.py
@@ -669,6 +669,7 @@ class Window:
             'env': self.child.environ,
             'cmdline': self.child.cmdline,
             'margin': self.margin.serialize(),
+            'user_vars': self.user_vars,
             'padding': self.padding.serialize(),
         }
         if self.window_custom_type: