diff -r c1fb2cab6260 -r f51713b8c6fa mercurial/error.py
--- a/mercurial/error.py	Thu Sep 24 15:52:11 2015 -0700
+++ b/mercurial/error.py	Thu Sep 24 10:53:16 2015 -0700
@@ -114,6 +114,10 @@
 class LockUnavailable(LockError):
     pass
 
+# LockError is for errors while acquiring the lock -- this is unrelated
+class LockInheritanceContractViolation(AssertionError):
+    pass
+
 class ResponseError(Exception):
     """Raised to print an error with part of output and exit."""