diff --git a/swh/journal/pytest_plugin.py b/swh/journal/pytest_plugin.py
--- a/swh/journal/pytest_plugin.py
+++ b/swh/journal/pytest_plugin.py
@@ -83,8 +83,9 @@
                 del value["ctime"]
 
         for key in known_keys:
+            str_key_error_msg = hash_to_hex(key) if not isinstance(key, dict) else key
             assert key in received_keys, (
-                f"expected {object_type} key {hash_to_hex(key)} "
+                f"expected {object_type} key {str_key_error_msg} "
                 "absent from consumed messages"
             )