diff --git a/ctapipe/core/config_writer.py b/ctapipe/core/config_writer.py
index 55bcd461c1f..75349d4b802 100644
--- a/ctapipe/core/config_writer.py
+++ b/ctapipe/core/config_writer.py
@@ -65,6 +65,11 @@ def commented(text, indent_level=indent_level, width=144):
     if isinstance(trait, traitlets.Unicode):
         trait_value = f"'{trait_value}'"
 
-    trait_repr += f"{indent_str*indent_level}{trait.name}: {trait_value}\n"
+    # Automatically comment all parameters that are unvalid
+    commented = ""
+    if trait_value == traitlets.Undefined:
+        commented = "#"
+
+    trait_repr += f"{indent_str*indent_level}{commented}{trait.name}: {trait_value}\n"
 
     return trait_repr