diff --git a/src/Numerics/Distributions/ChiSquared.cs b/src/Numerics/Distributions/ChiSquared.cs
index 53a2a7ba..4076a090 100644
--- a/src/Numerics/Distributions/ChiSquared.cs
+++ b/src/Numerics/Distributions/ChiSquared.cs
@@ -356,7 +356,7 @@ namespace MathNet.Numerics.Distributions
                 throw new ArgumentException(Resources.InvalidDistributionParameters);
             }
 
-            return SpecialFunctions.GammaLowerIncomplete(freedom/2.0, x/2.0)/SpecialFunctions.Gamma(freedom/2.0);
+            return SpecialFunctions.GammaLowerRegularized(freedom/2.0, x/2.0);
         }
 
         /// <summary>