diff --git a/src/borg/repository.py b/src/borg/repository.py
index 00a9c4e10..c83edcec8 100644
--- a/src/borg/repository.py
+++ b/src/borg/repository.py
@@ -96,6 +96,11 @@ class CheckNeeded(ErrorWithTraceback):
     class ObjectNotFound(ErrorWithTraceback):
         """Object with key {} not found in repository {}."""
 
+        def __init__(self, id, repo):
+            if isinstance(id, bytes):
+                id = bin_to_hex(id)
+            super().__init__(id, repo)
+
     def __init__(self, path, create=False, exclusive=False, lock_wait=None, lock=True, append_only=False):
         self.path = os.path.abspath(path)
         self._location = Location('file://%s' % self.path)