diff --git a/SecureCoding/SecureSerialization/KnownExploitableTypes.cs b/SecureCoding/SecureSerialization/KnownExploitableTypes.cs
index 171e4fd..bbcf269 100644
--- a/SecureCoding/SecureSerialization/KnownExploitableTypes.cs
+++ b/SecureCoding/SecureSerialization/KnownExploitableTypes.cs
@@ -78,7 +78,7 @@ public static bool IsKnownExploitableType(string typeFullName)
                 throw new ArgumentException(nameof(typeFullName));
             }
 
-return knownExploitableTypes.Exists(t => t.toLower().Contains(typeFullName.toLower()));
+return knownExploitableTypes.Exists(t => t.ToLowerInvariant().Contains(typeFullName.ToLowerInvariant()));
         }
 
         /// <summary>