diff --git a/specs/simple-serialize.md b/specs/simple-serialize.md
index 79ed0ef7b..0e0468eb7 100644
--- a/specs/simple-serialize.md
+++ b/specs/simple-serialize.md
@@ -119,7 +119,7 @@ Define value as an object that has properties `value.value` with the contained v
 
 ```python
 serialized_bytes = serialize(value.value)
-serialized_type_index = value.type_index.to_bytes(BYTES_PER_LENGTH_PREFIX, "little")
+serialized_type_index = value.type_index.to_bytes(BYTES_PER_LENGTH_OFFSET, "little")
 return serialized_type_index + serialized_bytes
 ```