--- a/mercurial/ui.py
+++ b/mercurial/ui.py
@@ -96,10 +96,12 @@ class ui(object):
     def _is_trusted(self, fp, f, warn=True):
         if not self.check_trusted:
             return True
+        st = util.fstat(fp)
+        if util.isowner(fp, st):
+            return True
         tusers = self.trusted_users
         tgroups = self.trusted_groups
         if (tusers or tgroups) and '*' not in tusers and '*' not in tgroups:
-            st = util.fstat(fp)
             user = util.username(st.st_uid)
             group = util.groupname(st.st_gid)
             if user not in tusers and group not in tgroups:

--- a/mercurial/util.py
+++ b/mercurial/util.py
@@ -654,6 +654,11 @@ if os.name == 'nt':
     def explain_exit(code):
         return _("exited with status %d") % code, code
 
+    # if you change this stub into a real check, please try to implement the
+    # username and groupname functions above, too.
+    def isowner(fp, st=None):
+        return True
+
     try:
         # override functions with win32 versions if possible
         from util_win32 import *
@@ -765,6 +770,16 @@ else:
             return _("stopped by signal %d") % val, val
         raise ValueError(_("invalid exit code"))
 
+    def isowner(fp, st=None):
+        """Return True if the file object f belongs to the current user.
+
+        The return value of a util.fstat(f) may be passed as the st argument.
+        """
+        if st is None:
+            st = fstat(f)
+        return st.st_uid == os.getuid()
+
+
 def opener(base, audit=True):
     """
     return a function that opens files relative to base

--- a/tests/test-trusted.py
+++ b/tests/test-trusted.py
@@ -41,6 +41,10 @@ def testui(user='foo', group='bar', tuse
         return group
     util.groupname = groupname
 
+    def isowner(fp, st=None):
+        return user == cuser
+    util.isowner = isowner
+
     # try to read everything
     #print '# File belongs to user %s, group %s' % (user, group)
     #print '# trusted users = %s; trusted groups = %s' % (tusers, tgroups)