diff --git a/src/Copar/Functors/MonoidValued.hs b/src/Copar/Functors/MonoidValued.hs
index fae0dc980adbd848042c30014c46ef43b42d1416..201e6753a49101416101d651a49df6eb865879d2 100644
--- a/src/Copar/Functors/MonoidValued.hs
+++ b/src/Copar/Functors/MonoidValued.hs
@@ -199,7 +199,7 @@ instance (Monoid m, Ord m) => RefinementInterface (SlowMonoidValued m) where
     let toS  = foldl' (flip SumBag.insert) SumBag.empty labels
         toCWithoutS = foldl' (flip SumBag.delete) counts labels
         sumS = fold toS
-        sumCWithoutS = fold toS
+        sumCWithoutS = fold toCWithoutS
         f3   = (sumRest, sumCWithoutS, sumS)
         w1   = (sumRest <> sumCWithoutS, toS)
         w2   = (sumRest <> sumS, toCWithoutS)