diff --git a/lambdas/s3hash/src/t4_lambda_s3hash/__init__.py b/lambdas/s3hash/src/t4_lambda_s3hash/__init__.py
index 7711564fb7b..70127560dd0 100644
--- a/lambdas/s3hash/src/t4_lambda_s3hash/__init__.py
+++ b/lambdas/s3hash/src/t4_lambda_s3hash/__init__.py
@@ -76,7 +76,7 @@ def sha256_chunked(cls, value: bytes):
     def for_parts(cls, checksums: T.Sequence[bytes]):
         return cls.sha256_chunked(hash_parts(checksums))
 
-    _EMPTY_HASH = hashlib.sha256().digest()
+    _EMPTY_HASH: T.ClassVar[bytes] = hashlib.sha256().digest()
 
     @classmethod
     def empty(cls):