diff --git a/swh/model/model.py b/swh/model/model.py
--- a/swh/model/model.py
+++ b/swh/model/model.py
@@ -203,6 +203,10 @@
     return hashlib.new("sha1", manifest).digest()
 
 
+def _compute_hash_from_manifest(manifest: bytes) -> Sha1Git:
+    return hashlib.new("sha1", manifest).digest()
+
+
 class HashableObject(metaclass=ABCMeta):
     """Mixin to automatically compute object identifier hash when
     the associated model is instantiated."""