diff --git a/authentic2_idp_cas/__init__.py b/authentic2_idp_cas/__init__.py
index ae88d52..575a7f0 100644
--- a/authentic2_idp_cas/__init__.py
+++ b/authentic2_idp_cas/__init__.py
@@ -1,6 +1,7 @@
 from django.utils.timezone import now
 from django.template.loader import render_to_string
 
+__version__ = '1.0'
 
 class Plugin(object):
     def get_before_urls(self):
diff --git a/setup.py b/setup.py
index 71b60cc..2fa8c01 100755
--- a/setup.py
+++ b/setup.py
@@ -2,8 +2,38 @@
 from setuptools import setup, find_packages
 import os
 
+def get_version():
+    import glob
+    import re
+    import os
+
+    version = None
+    for d in glob.glob('*'):
+        if not os.path.isdir(d):
+            continue
+        module_file = os.path.join(d, '__init__.py')
+        if not os.path.exists(module_file):
+            continue
+        for v in re.findall("""__version__ *= *['"](.*)['"]""",
+                open(module_file).read()):
+            assert version is None
+            version = v
+        if version:
+            break
+    assert version is not None
+    if os.path.exists('.git'):
+        import subprocess
+        p = subprocess.Popen(['git','describe','--dirty','--match=v*'],
+                stdout=subprocess.PIPE)
+        result = p.communicate()[0]
+        assert p.returncode == 0, 'git returned non-zero'
+        new_version = result.split()[0][1:]
+        assert new_version.split('-')[0] == version, '__version__ must match the last git annotated tag'
+        version = new_version.replace('-', '.')
+    return version
+
 setup(name='authentic2-idp-cas',
-        version='1.0',
+        version=get_version(),
         license='AGPLv3',
         description='Authentic2 IdP CAS',
         author="Entr'ouvert",