diff --git a/src/app_model/registries/_register.py b/src/app_model/registries/_register.py
index 2c92648..aeeb1e3 100644
--- a/src/app_model/registries/_register.py
+++ b/src/app_model/registries/_register.py
@@ -231,7 +231,9 @@ def my_action3():
             menus=menus,
             keybindings=keybindings,
         )
-    raise TypeError("'id_or_action' must be a string or an Action")
+    raise TypeError(
+        f"'id_or_action' must be a string or an Action not {type(id_or_action)}"
+    )
 
 
 def _register_action_str(