diff --git a/evmspec/data/_main.py b/evmspec/data/_main.py
index 6931e81..66dda85 100644
--- a/evmspec/data/_main.py
+++ b/evmspec/data/_main.py
@@ -298,7 +298,7 @@ def _decode_hook(typ: Type, obj: object):
 ONE_EMPTY_BYTE = bytes(HexBytes("0x00"))
 
 
-_MISSING_BYTES = {i: (32 - i) * ONE_EMPTY_BYTE for i in range(0, 32)}
+_MISSING_BYTES = {i: (32 - i) * ONE_EMPTY_BYTE for i in range(0, 33)}
 """Calculate the number of missing bytes and return them.
 
 Args:
@@ -340,7 +340,7 @@ def __new__(cls, v):
         try:
             missing_bytes = _MISSING_BYTES[len(input_bytes)]
         except KeyError as e:
-            raise ValueError(f"{v} is too long") from e.__cause__
+            raise ValueError(f"{v} is too long: {len(input_bytes)}") from e.__cause__
 
         return __hb_new__(cls, missing_bytes + input_bytes)