diff --git a/swh/loader/git/dumb.py b/swh/loader/git/dumb.py
--- a/swh/loader/git/dumb.py
+++ b/swh/loader/git/dumb.py
@@ -16,6 +16,8 @@
 from dulwich.pack import Pack, PackData, PackIndex, load_pack_index_file
 from urllib3.response import HTTPResponse
 
+from swh.loader.git.utils import HexBytes
+
 if TYPE_CHECKING:
     from .loader import RepoRepresentation
 
@@ -128,7 +130,7 @@
         buffer.seek(0)
         return buffer
 
-    def _get_refs(self) -> Dict[bytes, bytes]:
+    def _get_refs(self) -> Dict[bytes, HexBytes]:
         refs = {}
         refs_resp_bytes = self._http_get("info/refs")
         for ref_line in refs_resp_bytes.readlines():
@@ -136,7 +138,7 @@
             refs[ref_name] = ref_target
         return refs
 
-    def _get_head(self) -> Dict[bytes, bytes]:
+    def _get_head(self) -> Dict[bytes, HexBytes]:
         head_resp_bytes = self._http_get("HEAD")
         _, head_target = head_resp_bytes.readline().replace(b"\n", b"").split(b" ")
         return {b"HEAD": head_target}
diff --git a/swh/loader/git/loader.py b/swh/loader/git/loader.py
--- a/swh/loader/git/loader.py
+++ b/swh/loader/git/loader.py
@@ -35,6 +35,7 @@
 from swh.storage.interface import StorageInterface
 
 from . import converters, dumb, utils
+from .utils import HexBytes
 
 logger = logging.getLogger(__name__)
 
@@ -53,7 +54,7 @@
         else:
             self.base_snapshot = Snapshot(branches={})
 
-        self.heads: Set[bytes] = set()
+        self.heads: Set[HexBytes] = set()
 
     def get_parents(self, commit: bytes) -> List[bytes]:
         """This method should return the list of known parents"""
@@ -62,7 +63,7 @@
     def graph_walker(self) -> ObjectStoreGraphWalker:
         return ObjectStoreGraphWalker(self.heads, self.get_parents)
 
-    def determine_wants(self, refs: Dict[bytes, bytes]) -> List[bytes]:
+    def determine_wants(self, refs: Dict[bytes, HexBytes]) -> List[HexBytes]:
         """Get the list of bytehex sha1s that the git loader should fetch.
 
         This compares the remote refs sent by the server with the base snapshot
@@ -73,7 +74,7 @@
             return []
 
         # Cache existing heads
-        local_heads: Set[bytes] = set()
+        local_heads: Set[HexBytes] = set()
         for branch_name, branch in self.base_snapshot.branches.items():
             if not branch or branch.target_type == TargetType.ALIAS:
                 continue
@@ -82,7 +83,7 @@
         self.heads = local_heads
 
         # Get the remote heads that we want to fetch
-        remote_heads: Set[bytes] = set()
+        remote_heads: Set[HexBytes] = set()
         for ref_name, ref_target in refs.items():
             if utils.ignore_branch_name(ref_name):
                 continue
@@ -93,8 +94,8 @@
 
 @dataclass
 class FetchPackReturn:
-    remote_refs: Dict[bytes, bytes]
-    symbolic_refs: Dict[bytes, bytes]
+    remote_refs: Dict[bytes, HexBytes]
+    symbolic_refs: Dict[bytes, HexBytes]
     pack_buffer: SpooledTemporaryFile
     pack_size: int
 
@@ -136,8 +137,8 @@
         self.pack_size_bytes = pack_size_bytes
         self.temp_file_cutoff = temp_file_cutoff
         # state initialized in fetch_data
-        self.remote_refs: Dict[bytes, bytes] = {}
-        self.symbolic_refs: Dict[bytes, bytes] = {}
+        self.remote_refs: Dict[bytes, HexBytes] = {}
+        self.symbolic_refs: Dict[bytes, HexBytes] = {}
         self.ref_object_types: Dict[bytes, Optional[TargetType]] = {}
 
     def fetch_pack_from_origin(
@@ -283,7 +284,7 @@
             logger.debug("Fetching objects with HTTP dumb transfer protocol")
             self.dumb_fetcher = dumb.GitObjectsFetcher(self.origin_url, base_repo)
             self.dumb_fetcher.fetch_object_ids()
-            self.remote_refs = utils.filter_refs(self.dumb_fetcher.refs)
+            self.remote_refs = utils.filter_refs(self.dumb_fetcher.refs)  # type: ignore
             self.symbolic_refs = self.dumb_fetcher.head
         else:
             self.pack_buffer = fetch_info.pack_buffer
diff --git a/swh/loader/git/utils.py b/swh/loader/git/utils.py
--- a/swh/loader/git/utils.py
+++ b/swh/loader/git/utils.py
@@ -1,4 +1,4 @@
-# Copyright (C) 2017-2020  The Software Heritage developers
+# Copyright (C) 2017-2021  The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
@@ -10,11 +10,14 @@
 import os
 import shutil
 import tempfile
-from typing import Dict, Optional
+from typing import Dict, NewType, Optional
 
 from swh.core import tarball
 from swh.model.model import SnapshotBranch
 
+# The hexadecimal representation of the hash in bytes
+HexBytes = NewType("HexBytes", bytes)
+
 
 def init_git_repo_from_archive(project_name, archive_path, root_temp_dir="/tmp"):
     """Given a path to an archive containing a git repository.
@@ -90,10 +93,12 @@
     return False
 
 
-def filter_refs(refs: Dict[bytes, bytes]) -> Dict[bytes, bytes]:
+def filter_refs(refs: Dict[bytes, bytes]) -> Dict[bytes, HexBytes]:
     """Filter the refs dictionary using the policy set in `ignore_branch_name`"""
     return {
-        name: target for name, target in refs.items() if not ignore_branch_name(name)
+        name: HexBytes(target)
+        for name, target in refs.items()
+        if not ignore_branch_name(name)
     }