diff --git a/swh/loader/package/debian/loader.py b/swh/loader/package/debian/loader.py
--- a/swh/loader/package/debian/loader.py
+++ b/swh/loader/package/debian/loader.py
@@ -89,31 +89,38 @@
         yield release_name(version), p_info
 
     def resolve_revision_from(
-            self, known_package_artifacts: Dict, artifact_metadata: Dict) \
+            self, known_package_artifacts: Mapping,
+            artifact_metadata: Mapping[str, Any]) \
             -> Optional[bytes]:
-        artifacts_to_fetch = artifact_metadata['files']
-        logger.debug('k_p_artifacts: %s', known_package_artifacts)
-        logger.debug('artifacts_to_fetch: %s', artifacts_to_fetch)
-        for rev_id, known_artifacts in known_package_artifacts.items():
-            logger.debug('Revision: %s', rev_id)
-            logger.debug('Associated known_artifacts: %s', known_artifacts)
-            known_artifacts = known_artifacts['extrinsic']['raw']['files']
-            rev_found = True
-            for a_name, k_artifact in known_artifacts.items():
-                artifact_to_fetch = artifacts_to_fetch.get(a_name)
-                logger.debug('artifact_to_fetch: %s', artifact_to_fetch)
-                if artifact_to_fetch is None:
-                    # as soon as we do not see an artifact, we consider we need
-                    # to check the other revision
-                    rev_found = False
-                if k_artifact['sha256'] != artifact_to_fetch['sha256']:
-                    # Hash is different, we consider we need to check the other
-                    # revisions
-                    rev_found = False
-            if rev_found:
-                logger.debug('Existing revision %s found for new artifacts.',
-                             rev_id)
-                return rev_id
+        try:
+            artifacts_to_fetch = artifact_metadata['files']
+            logger.debug('k_p_artifacts: %s', known_package_artifacts)
+            logger.debug('artifacts_to_fetch: %s', artifacts_to_fetch)
+            for rev_id, known_artifacts in known_package_artifacts.items():
+                logger.debug('Revision: %s', rev_id)
+                logger.debug('Associated known_artifacts: %s', known_artifacts)
+                known_artifacts = known_artifacts['extrinsic']['raw']['files']
+                rev_found = False
+                for a_name, k_artifact in known_artifacts.items():
+                    artifact_to_fetch = artifacts_to_fetch.get(a_name)
+                    logger.debug('artifact_to_fetch: %s', artifact_to_fetch)
+                    if artifact_to_fetch is None:
+                        # as soon as we do not see an artifact, we consider we
+                        # need to check the other revision
+                        continue
+                    if k_artifact['sha256'] == artifact_to_fetch['sha256']:
+                        # Hash is different, we consider we need to check the
+                        # other revisions
+                        rev_found = True
+                        break
+                if rev_found:
+                    logger.debug(
+                        'Existing revision %s found for new artifacts.',
+                        rev_id)
+                    return rev_id
+        except KeyError as e:
+            logger.warning(
+                'Older revision format detected. Reason: Missing key %s', e)
         logger.debug('No existing revision found for the new artifacts.')
         return None