diff --git a/C5.Tests/SupportClasses.cs b/C5.Tests/SupportClasses.cs
index 470342bb..97fe5936 100644
--- a/C5.Tests/SupportClasses.cs
+++ b/C5.Tests/SupportClasses.cs
@@ -3,18 +3,28 @@
 
 using NUnit.Framework;
 using System;
+using System.Diagnostics.CodeAnalysis;
 using SCG = System.Collections.Generic;
 
 
 namespace C5.Tests
 {
-    internal class SC : SCG.IComparer<string>
+    internal class SC : SCG.IComparer<string>, SCG.IEqualityComparer<string>
     {
         public int Compare(string a, string b)
         {
             return a.CompareTo(b);
         }
 
+        public bool Equals(string x, string y)
+        {
+            return StringComparer.Ordinal.Equals(x, y);
+        }
+
+        public int GetHashCode(string obj)
+        {
+            return StringComparer.Ordinal.GetHashCode(obj);
+        }
 
         public void appl(String s)
         {