diff --git a/acquire/tools/decrypter.py b/acquire/tools/decrypter.py
index 6178d23..8720fba 100644
--- a/acquire/tools/decrypter.py
+++ b/acquire/tools/decrypter.py
@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 import argparse
 import base64
 import contextlib
@@ -220,7 +222,7 @@ def timestamp(self) -> datetime:
         return datetime.fromtimestamp(self.file_header.timestamp, timezone.utc)
 
 
-def decrypt_header(header, fingerprint: bytes, key_file=Path | None, key_server=str | None) -> bytes:
+def decrypt_header(header, fingerprint: bytes, key_file: Path | None, key_server: str | None) -> bytes:
     if not key_file and not key_server:
         raise ValueError("Need either key file or key server")