diff --git a/swh/storage/validate.py b/swh/storage/validate.py
--- a/swh/storage/validate.py
+++ b/swh/storage/validate.py
@@ -30,7 +30,7 @@
     try:
         yield
     except VALIDATION_EXCEPTIONS as e:
-        raise StorageArgumentException(*e.args)
+        raise StorageArgumentException(str(e))
 
 
 class ValidatingProxyStorage: