diff --git a/mercurial/state.py b/mercurial/state.py
--- a/mercurial/state.py
+++ b/mercurial/state.py
@@ -51,6 +51,7 @@
             self.opts = {}
         else:
             self.opts = opts
+        self.opts['magicheader'] = 'HGStateFile'
 
     def __nonzero__(self):
         return self.exists()