diff --git a/mercurial/context.py b/mercurial/context.py
--- a/mercurial/context.py
+++ b/mercurial/context.py
@@ -128,6 +128,16 @@ class basectx(object):
                               include, exclude, default,
                               auditor=r.auditor, ctx=self)
 
+    def diff(self, ctx2=None, match=None, **opts):
+        """Returns a diff generator for the given contexts and matcher"""
+        if ctx2 is None:
+            ctx2 = self.p1()
+        if ctx2 is not None and not isinstance(ctx2, changectx):
+            ctx2 = self._repo[ctx2]
+        diffopts = patch.diffopts(self._repo.ui, opts)
+        return patch.diff(self._repo, ctx2.node(), self.node(),
+                          match=match, opts=diffopts)
+
 class changectx(basectx):
     """A changecontext object makes access to data related to a particular
     changeset convenient. It represents a read-only context already presnt in
@@ -389,16 +399,6 @@ class changectx(basectx):
             if match.bad(fn, _('no such file in rev %s') % self) and match(fn):
                 yield fn
 
-    def diff(self, ctx2=None, match=None, **opts):
-        """Returns a diff generator for the given contexts and matcher"""
-        if ctx2 is None:
-            ctx2 = self.p1()
-        if ctx2 is not None and not isinstance(ctx2, changectx):
-            ctx2 = self._repo[ctx2]
-        diffopts = patch.diffopts(self._repo.ui, opts)
-        return patch.diff(self._repo, ctx2.node(), self.node(),
-                          match=match, opts=diffopts)
-
     @propertycache
     def _dirs(self):
         return scmutil.dirs(self._manifest)