diff --git a/dangerzone/updater/signatures.py b/dangerzone/updater/signatures.py
index 57b3d1d..7591631 100644
--- a/dangerzone/updater/signatures.py
+++ b/dangerzone/updater/signatures.py
@@ -383,7 +383,7 @@ def get_remote_signatures(image: str, digest: str) -> List[Dict]:
     return signatures
 
 
-def prepare_airgapped_archive(image_name, destination):
+def prepare_airgapped_archive(image_name: str, destination: str):
     if "@sha256:" not in image_name:
         raise errors.AirgappedImageDownloadError(
             "The image name must include a digest, e.g. ghcr.io/freedomofpress/dangerzone/dangerzone@sha256:123456"