diff --git a/mercurial/registrar.py b/mercurial/registrar.py
--- a/mercurial/registrar.py
+++ b/mercurial/registrar.py
@@ -166,7 +166,8 @@
     DoS attack (False by default).
 
     Optional argument 'takeorder' indicates whether a predicate function
-    takes ordering policy as the last argument.
+    takes ordering policy as the last argument. By default, takeorder is None
+    and will be inferrepo from function signature.
 
     Optional argument 'takesubset' indicates whether a predicate function
     takes subset as its second argument. By default, takesubset is None and
@@ -188,8 +189,12 @@
     _getname = _funcregistrarbase._parsefuncdecl
     _docformat = "``%s``\n    %s"
 
-    def _extrasetup(self, name, func, safe=False, takeorder=False,
+    def _extrasetup(self, name, func, safe=False, takeorder=None,
                     takesubset=None):
+        args = inspect.getargspec(func).args
+        if takeorder is None:
+            takeorder = (len(args) >= 4)
+
         if takeorder:
             if takesubset is False:
                 raise error.ProgrammingError(
@@ -198,7 +203,6 @@
 
         if takesubset is None:
             # detect from signature
-            args = inspect.getargspec(func).args
             takesubset = (len(args) >= 3)
 
         func._safe = safe
diff --git a/mercurial/revset.py b/mercurial/revset.py
--- a/mercurial/revset.py
+++ b/mercurial/revset.py
@@ -65,7 +65,7 @@
 
     A typical use of this function is::
 
-        @revsetpredicate('myrevset', takeorder=True)
+        @revsetpredicate('myrevset')
         def myrevset(repo, subset, x, order):
             newset = ...  # a smartset that implements "myrevset"
             return revset.intersect(subset, newset, order)