diff --git a/lib/ast.js b/lib/ast.js
index b73d2ebe..4d8b1431 100644
--- a/lib/ast.js
+++ b/lib/ast.js
@@ -47,21 +47,22 @@ function DEFNODE(type, props, methods, base) {
     if (arguments.length < 4) base = AST_Node;
     if (!props) props = [];
     else props = props.split(/\s+/);
-    var ctor = function (props) {
-        if (props) {
-            var ctor = this.CTOR;
-            do {
-                var self_props = ctor.SELF_PROPS;
-                for (var i = self_props.length; i;) {
-                    var k = self_props[--i];
-                    this[k] = props[k];
-                }
-            } while (ctor = ctor.BASE)
-            if (this.initialize) {
-                this.initialize();
-            }
-        }
-    }
+    var code = "return function AST_" + type + "(props) {\
+        if (props) {\
+            var ctor = this.CTOR;\
+            do {\
+                var self_props = ctor.SELF_PROPS;\
+                for (var i = self_props.length; i;) {\
+                    var k = self_props[--i];\
+                    this[k] = props[k];\
+                }\
+            } while (ctor = ctor.BASE);\
+            if (this.initialize) {\
+                this.initialize();\
+            }\
+        }\
+    }";
+    var ctor = new Function(code)();
     var proto = base && new base;
     if (proto) {
         ctor.prototype = proto;