diff --git a/modules/mol/alg/pymod/chain_mapping.py b/modules/mol/alg/pymod/chain_mapping.py
index 7573286c8441e0a2b94a4facb136c0b5dd908a89..c2d16bc044e4d8933d3b32e061b4794bff25c1a2 100644
--- a/modules/mol/alg/pymod/chain_mapping.py
+++ b/modules/mol/alg/pymod/chain_mapping.py
@@ -2388,7 +2388,7 @@ class _QSScoreGreedySearcher(qsscore.QSScorer):
 
         # try all possible mapping swaps. Swaps that improve the score are
         # immediately accepted and we start all over again
-        nominator, denominator = self._fromFlatMapping(mapping)
+        nominator, denominator = self._FromFlatMapping(mapping)
         current_score = 0.0
         if denominator != 0.0:
             current_score = nominator / denominator