diff --git a/lib/std.js b/lib/std.js
index eac9332..1fb78cb 100644
--- a/lib/std.js
+++ b/lib/std.js
@@ -430,6 +430,15 @@ function AsyncFunction(f, __filename) {
     this.runSynchronously = function() {
         return this.f.apply(null, arguments);
     };
+
+    if (typeof this.__filename === "string") {
+        this.__filename = __filename;
+    } else if (typeof WScript !== "undefined") {
+        this.__filename = (function(path) {
+            var pos = Math.max.apply(null, [path.lastIndexOf("\\"), path.lastIndexOf("/")]);
+            return (pos > -1 ? path.substring(pos + 1) : "");
+        })(WScript.ScriptFullName);
+    }
 };
 AsyncFunction.counter = 0;
 AsyncFunction.bind = function(exports, args) {