diff --git a/python/podio/frame.py b/python/podio/frame.py
index 942c53135..4031ce92d 100644
--- a/python/podio/frame.py
+++ b/python/podio/frame.py
@@ -264,6 +264,8 @@ def put_parameter(self, key, value, as_type=None):
                 cpp_types = _get_cpp_types(as_type)
                 if len(cpp_types) == 0:
                     raise ValueError(f"Cannot put a parameter of type {as_type} into a Frame")
+                # The first [0] gets the tuple, the second [0] gets the actual C++ type
+                # from SUPPORTED_PARAMETER_TYPES
                 self._frame.putParameter[cpp_types[0][0]](key, value)
 
             # If we have a single integer, a std::string overload kicks in with higher