diff --git a/tools/build/build.py b/tools/build/build.py
index b61eef0b..a2387102 100755
--- a/tools/build/build.py
+++ b/tools/build/build.py
@@ -7,6 +7,7 @@ import os
 import ox
 import re
 import shutil
+import subprocess
 import sys
 
 
@@ -19,8 +20,11 @@ def build_oxjs(geo):
     source_path = '../../source/'
     build_path = '../../build/'
     dev_path = '../../dev/'
-    comment = 'OxJS (c) 2012 0x2620, dual-licensed GPL/MIT, see http://oxjs.org for details'
-
+    version = '0.1.%s' % subprocess.Popen(
+        ['bzr', 'revno'],
+        stdout=subprocess.PIPE
+    ).communicate()[0].strip()
+    comment = 'OxJS %s (c) 2012 0x2620, dual-licensed GPL/MIT, see http://oxjs.org for details' % version
     # SVGs
     path = source_path + 'Ox.UI/themes/classic/svg/'
     for filename in os.listdir(path):
@@ -100,6 +104,7 @@ def build_oxjs(geo):
         js += read_file(source_path + js_dir + filename) + '\n'
         if not js_dir + filename in data[0] + data[1]:
             data[2].append(js_dir + filename)
+    js = js.replace("Ox.VERSION = '0.1.2';", "Ox.VERSION = '%s';" % version)
     write_file(build_path + 'Ox.js', ox.js.minify(js, comment))
     write_file(dev_path + '/Ox/json/' + 'Ox.json', json.dumps(data, indent=4))