diff --git a/src/Numerics/Distributions/Zipf.cs b/src/Numerics/Distributions/Zipf.cs
index 5f1aa397..0784d672 100644
--- a/src/Numerics/Distributions/Zipf.cs
+++ b/src/Numerics/Distributions/Zipf.cs
@@ -270,7 +270,7 @@ namespace MathNet.Numerics.Distributions
         /// <returns>the cumulative distribution at location <paramref name="x"/>.</returns>
         public double CumulativeDistribution(double x)
         {
-            if (x <= 1)
+            if (x < 1)
             {
                 return 0.0;
             }