diff --git a/mercurial/dispatch.py b/mercurial/dispatch.py
--- a/mercurial/dispatch.py
+++ b/mercurial/dispatch.py
@@ -488,7 +488,7 @@
         return aliasargs(self.fn, args)
 
     def __getattr__(self, name):
-        adefaults = {r'norepo': True,
+        adefaults = {r'norepo': True, r'cmdtype': 'unrecoverable',
                      r'optionalrepo': False, r'inferrepo': False}
         if name not in adefaults:
             raise AttributeError(name)
diff --git a/mercurial/registrar.py b/mercurial/registrar.py
--- a/mercurial/registrar.py
+++ b/mercurial/registrar.py
@@ -7,6 +7,8 @@
 
 from __future__ import absolute_import
 
+from .i18n import _
+
 from . import (
     configitems,
     error,
@@ -149,9 +151,14 @@
     def _doregister(self, func, name, options=(), synopsis=None,
                     norepo=False, optionalrepo=False, inferrepo=False,
                     cmdtype=cmdtype.UNRECOVERABLE_WRITE):
+        possiblecmdtypes = set(['unrecoverable', 'recoverable', 'readonly'])
         func.norepo = norepo
         func.optionalrepo = optionalrepo
         func.inferrepo = inferrepo
+        if cmdtype not in possiblecmdtypes:
+            raise error.ProgrammingError(_("unknown cmdtype value '%s' for "
+                                            "'%s' command") % (cmdtype, name))
+        func.cmdtype = cmdtype
         if synopsis:
             self._table[name] = func, list(options), synopsis
         else: