diff -r a3eb8b0dfb81 -r 7b379a47e3a9 rt/vm/src/main/java/org/apidesign/vm4brwsr/ByteCodeToJavaScript.java
--- a/rt/vm/src/main/java/org/apidesign/vm4brwsr/ByteCodeToJavaScript.java	Fri Jul 12 16:06:38 2013 +0200
+++ b/rt/vm/src/main/java/org/apidesign/vm4brwsr/ByteCodeToJavaScript.java	Thu Sep 05 09:36:06 2013 +0200
@@ -208,14 +208,18 @@
             out.append("\n    ").append(destObject).append(".").append(mn).append(".cls = CLS;");
         }
         out.append("\n    c.constructor = CLS;");
+        out.append("\n    function fillInstOf(x) {");
         String instOfName = "$instOf_" + className;
-        out.append("\n    c.").append(instOfName).append(" = true;");
+        out.append("\n        x.").append(instOfName).append(" = true;");
+        for (String superInterface : jc.getSuperInterfaces()) {
+            String intrfc = superInterface.replace('/', '_');
+            out.append("\n      vm.").append(intrfc).append("(false).fillInstOf(x);");
+            requireReference(superInterface);
+        }
+        out.append("\n    }");
+        out.append("\n    c.fillInstOf = fillInstOf;");
+        out.append("\n    fillInstOf(c);");
         obfuscationDelegate.exportJSProperty(out, "c", instOfName);
-        for (String superInterface : jc.getSuperInterfaces()) {
-            instOfName = "$instOf_" + superInterface.replace('/', '_');
-            out.append("\n    c.").append(instOfName).append(" = true;");
-            obfuscationDelegate.exportJSProperty(out, "c", instOfName);
-        }
         out.append("\n    CLS.$class = 'temp';");
         out.append("\n    CLS.$class = ");
         out.append(accessClass("java_lang_Class(true);"));