diff --git a/rhino/fs.js b/rhino/fs.js
index ee809598..2b6c0390 100644
--- a/rhino/fs.js
+++ b/rhino/fs.js
@@ -162,7 +162,7 @@ exports.copyFileSync = function(inFile, outDir, fileName) {
 };
 
 exports.writeFileSync = function(filename, data, encoding) {
-    encoding = checkEncoding(encoding);
+    encoding = checkEncoding(encoding, 'fs.writeFileSync');
 
     var out = new Packages.java.io.PrintWriter(
         new Packages.java.io.OutputStreamWriter(