diff --git a/unpacked/extensions/TeX/bbox.js b/unpacked/extensions/TeX/bbox.js
index cb26e280d..594b7e7c7 100644
--- a/unpacked/extensions/TeX/bbox.js
+++ b/unpacked/extensions/TeX/bbox.js
@@ -46,7 +46,7 @@
  */
 
 MathJax.Extension["TeX/bbox"] = {
-  version: "2.3"
+  version: "2.3.1"
 };
 
 MathJax.Hub.Register.StartupHook("TeX Jax Ready",function () {
@@ -61,7 +61,7 @@ MathJax.Hub.Register.StartupHook("TeX Jax Ready",function () {
       var bbox = this.GetBrackets(name,""),
           math = this.ParseArg(name);
       var parts = bbox.split(/,/), def, background, style;
-      for (var i in parts) {
+      for (var i = 0, m = parts.length; i < m; i++) {
         var part = parts[i].replace(/^\s+/,'').replace(/\s+$/,'');
         var match = part.match(/^(\.\d+|\d+(\.\d*)?)(pt|em|ex|mu|px|in|cm|mm)$/);
         if (match) {