diff --git a/setup.py b/setup.py
--- a/setup.py
+++ b/setup.py
@@ -181,7 +181,10 @@
     # error 0xc0150004. See: http://bugs.python.org/issue3440
     env['SystemRoot'] = os.environ['SystemRoot']
 
-if os.path.isdir('.hg'):
+if os.path.exists('.hg_force_version'):
+    with open('.hg_force_version') as f:
+        version = f.read().rstrip('\n')
+elif os.path.isdir('.hg'):
     cmd = [sys.executable, 'hg', 'log', '-r', '.', '--template', '{tags}\n']
     numerictags = [t for t in runhg(cmd, env).split() if t[0].isdigit()]
     hgid = runhg([sys.executable, 'hg', 'id', '-i'], env).strip()