diff --git a/lib/ast.js b/lib/ast.js
index 99415446..8382495c 100644
--- a/lib/ast.js
+++ b/lib/ast.js
@@ -93,8 +93,9 @@ var AST_Token = DEFNODE("Token", "type value line col pos endline endcol endpos
 var AST_Node = DEFNODE("Node", "start end", {
     _clone: function(deep, depth) {
         if (typeof depth == "undefined") depth = 0;
-        if (depth++ > 1000) {
-            throw new Error("clone depth exceeded (" + this.start.line + ", " + this.start.col + ")");
+        if (depth++ > 500) {
+            throw new Error("maximum clone depth exceeded (" +
+                this.start.file + ":" + this.start.line + ":" + this.start.col + ")");
         }
         if (deep) {
             var self = this.clone(false, depth);