diff --git a/Octokit/Helpers/StringExtensions.cs b/Octokit/Helpers/StringExtensions.cs
index 50e41f36..282653eb 100644
--- a/Octokit/Helpers/StringExtensions.cs
+++ b/Octokit/Helpers/StringExtensions.cs
@@ -80,19 +80,19 @@ namespace Octokit
             Justification = "Ruby don't care. Ruby don't play that.")]
         public static string ToRubyCase(this string propertyName)
         {
-            Ensure.ArgumentNotNullOrEmptyString(propertyName, "s");
+            Ensure.ArgumentNotNullOrEmptyString(propertyName, "propertyName");
             return string.Join("_", propertyName.SplitUpperCase()).ToLowerInvariant();
         }
 
         public static string FromRubyCase(this string propertyName)
         {
-            Ensure.ArgumentNotNullOrEmptyString(propertyName, "s");
+            Ensure.ArgumentNotNullOrEmptyString(propertyName, "propertyName");
             return string.Join("", propertyName.Split('_')).ToCapitalizedInvariant();
         }
 
         public static string ToCapitalizedInvariant(this string value)
         {
-            Ensure.ArgumentNotNullOrEmptyString(value, "s");
+            Ensure.ArgumentNotNullOrEmptyString(value, "value");
             return string.Concat(value[0].ToString().ToUpperInvariant(), value.Substring(1));
         }
         static IEnumerable<string> SplitUpperCase(this string source)