diff --git a/obo/obo.py b/obo/obo.py
index 71a05cc..1216c90 100644
--- a/obo/obo.py
+++ b/obo/obo.py
@@ -426,7 +426,7 @@ def replace(self, source, version_id):
         headers['x-amz-copy-source'] = src_str
         headers['x-amz-metadata-directive'] = 'REPLACE'
 
-        for (h, v) in k.metadata:
+        for (h, v) in k.metadata.items():
             headers[h] = v;
 
         if k.content_type: