diff --git a/swh/loader/core/loader.py b/swh/loader/core/loader.py
--- a/swh/loader/core/loader.py
+++ b/swh/loader/core/loader.py
@@ -280,7 +280,7 @@
                 'swh_id': log_id
             })
 
-        tools = self.storage.tool_add([tool])
+        tools = list(self.storage.tool_add([tool]))
         tool_id = tools[0]['id']
 
         self.log.debug(