diff --git a/src/pyrad3/utils.py b/src/pyrad3/utils.py
index be6bfcb..291f88a 100644
--- a/src/pyrad3/utils.py
+++ b/src/pyrad3/utils.py
@@ -65,7 +65,6 @@ def decode_attributes(
 
     for key, value, offset in pre_decode_attributes(rad_dict, packet):
         attr_def = rad_dict.attrindex.get(key)
-        length = len(value)
         dec_value: Any = value  # to silence mypy
         tag = 0
         if attr_def is None:
@@ -82,6 +81,7 @@ def decode_attributes(
                 dec_value = attr_def.values[dec_value]
             except KeyError:
                 pass
+        length = len(value)
         attributes.append(
             Attribute(
                 name=name,