diff --git a/doc/python/mechanisms.rst b/doc/python/mechanisms.rst
index dbeb7903106c8a1e9a3240b1468acf8ad0adafad..97b9312cc94f34d150add05f905823e9ccb66252 100644
--- a/doc/python/mechanisms.rst
+++ b/doc/python/mechanisms.rst
@@ -464,7 +464,8 @@ Mechanism catalogues
 
     .. py:method:: extend(other, prefix)
 
-        Import another catalogue, possibly with a prefix. Will overwrite in case of name collisions.
+        Import another catalogue, possibly with a prefix. Will raise an exception
+        in case of name collisions.
 
         .. code-block:: Python