diff --git a/plone/app/discussion/catalog.py b/plone/app/discussion/catalog.py
index 84691c5..20310ea 100644
--- a/plone/app/discussion/catalog.py
+++ b/plone/app/discussion/catalog.py
@@ -36,7 +36,7 @@ def last_comment_date(object):
 @indexer(IContentish, IZCatalog)
 def commentators(object):
     conversation = IConversation(object)
-    return tuple(set(conversation.commentators.keys()))
+    return tuple(conversation.commentators.keys())
 
 # Comment Indexers