diff --git a/preparator.py b/preparator.py
index f9ac0c7..a705a5c 100644
--- a/preparator.py
+++ b/preparator.py
@@ -169,7 +169,9 @@ def get_sets(mentions):
     all_mentions = []
     clustered_mensions = []
     for mention in mentions:
-        all_mentions.append(mention.attrib['span'])
+        if not mention.attrib['mention_head'] in POSSIBLE_HEADS:
+            all_mentions.append(mention.attrib['span'])
+        
         set_id = mention.attrib['mention_group']
         if set_id == 'empty' or set_id == '' or mention.attrib['mention_head'] in POSSIBLE_HEADS:
             pass