diff --git a/kitty/layout/tall.py b/kitty/layout/tall.py
index d2e9278c6..9f595d532 100644
--- a/kitty/layout/tall.py
+++ b/kitty/layout/tall.py
@@ -79,7 +79,7 @@ class TallLayoutOpts(LayoutOpts):
         self.mirrored = to_bool(data.get('mirrored', 'false'))
 
     def serialized(self) -> dict[str, Any]:
-        return {'full_size': self.full_size, 'bias': self.bias, 'mirrored': self.mirrored}
+        return {'full_size': self.full_size, 'bias': self.bias, 'mirrored': 'y' if self.mirrored else 'n'}
 
     def build_bias_list(self) -> tuple[float, ...]:
         b = self.bias / 100