diff --git a/Tests/FluentAssertions.Specs/Collections/CollectionAssertionSpecs.cs b/Tests/FluentAssertions.Specs/Collections/CollectionAssertionSpecs.cs
index e539aacad..b908e6669 100644
--- a/Tests/FluentAssertions.Specs/Collections/CollectionAssertionSpecs.cs
+++ b/Tests/FluentAssertions.Specs/Collections/CollectionAssertionSpecs.cs
@@ -218,7 +218,7 @@ private class ByLastCharacterComparer : IComparer<string>
     {
         public int Compare(string x, string y)
         {
-            return x[^1].CompareTo(y[^1]);
+            return Nullable.Compare(x?[^1], y?[^1]);
         }
     }
 }