diff --git a/lib/std.js b/lib/std.js
index 3d8a4d8..72276f4 100644
--- a/lib/std.js
+++ b/lib/std.js
@@ -342,15 +342,23 @@ function AsyncFunction(f) {
     this.f = f;
 
     this.run = function() {
+		AsyncFunction.counter++;    // increase number of async functions
+
+        var _this = this;
+        var f = function() {
+            _this.f();
+            AsyncFunction.counter--;    // decrease number of async functions
+        };
+
         if (this.proxyWindow != null) {
             try {
-                this.proxyWindow.setTimeout(1, this.f);
+                this.proxyWindow.setTimeout(1, f);
             } catch (e) {
                 console.warn("AsyncFunction proxyWindow.setTimeout failed:", e.message);
-                sleep(1, this.f);
+                sleep(1, f);
             }
         } else {
-            sleep(1, this.f);
+            sleep(1, f);
         }
     };
 
@@ -368,6 +376,7 @@ function AsyncFunction(f) {
         }
     }
 };
+AsyncFunction.counter = 0;    // static variable
 
 global.GetResource = GetResource;
 global.sleep = sleep;