diff --git a/Utilities.cs b/Utilities.cs
index 1bb1ce7..a52e368 100644
--- a/Utilities.cs
+++ b/Utilities.cs
@@ -129,7 +129,7 @@ internal static string DecodeBase64(string data, Encoding encoding = null) {
     }
 
     #region OpenPOP.NET
-    internal static string DecodeWords(string encodedWords, Encoding @default) {
+    internal static string DecodeWords(string encodedWords, Encoding @default = null) {
       if (string.IsNullOrEmpty(encodedWords))
         return string.Empty;