diff --git a/patacrep/templates.py b/patacrep/templates.py
index f86b1d99..370b3d88 100644
--- a/patacrep/templates.py
+++ b/patacrep/templates.py
@@ -147,7 +147,7 @@ class TexBookRenderer(Renderer):
     def _get_variables(parameter, user_config):
         '''Get the default value for the parameter, according to the language.
         '''
-        schema = parameter.get('schema', {}).copy()
+        schema = parameter.get('schema', {})
 
         data = utils.DictOfDict(parameter.get('default', {}))
         data.update(user_config)