diff --git a/smodels/matching/clusterTools.py b/smodels/matching/clusterTools.py
index 79b6cc4f3..ef6a59f2c 100644
--- a/smodels/matching/clusterTools.py
+++ b/smodels/matching/clusterTools.py
@@ -107,6 +107,9 @@ def __cmp__(self, other):
 
         if not isinstance(other, TheorySMS):
             return -1
+        
+        if self.canonName != other.canonName:
+            return -1
 
         for nodeIndex in self.nodeIndices:
             nodeA = self.indexToNode(nodeIndex)