diff --git a/plugins/User/plugin.py b/plugins/User/plugin.py
index 8ba41b702..d8f4b0a38 100644
--- a/plugins/User/plugin.py
+++ b/plugins/User/plugin.py
@@ -321,6 +321,7 @@ class User(callbacks.Plugin):
             must be sent to the bot privately (not on a channel) since it may
             contain a password.
             """
+            caller_is_owner = ircdb.checkCapability(msg.prefix, 'owner')
             if not hostmask:
                 hostmask = msg.prefix
             if not ircutils.isUserHostmask(hostmask):
@@ -335,15 +336,17 @@ class User(callbacks.Plugin):
             try:
                 otherId = ircdb.users.getUserId(hostmask)
                 if otherId != user.id:
-                    irc.error(_('That hostmask is already registered.'),
-                              Raise=True)
+                    if caller_is_owner:
+                        err = _('That hostmask is already registered to %s.')
+                        err %= otherId
+                    else:
+                        err = _('That hostmask is already registered.')
+                    irc.error(err, Raise=True)
             except KeyError:
                 pass
             if not user.checkPassword(password) and \
-               not user.checkHostmask(msg.prefix):
-                if ircdb.checkCapability(msg.prefix, 'owner'):
-                    u = ircdb.users.getUser(msg.prefix)
-                else:
+               not user.checkHostmask(msg.prefix) and \
+               not caller_is_owner:
                     irc.error(conf.supybot.replies.incorrectAuthentication(),
                               Raise=True)
             try:
@@ -352,10 +355,14 @@ class User(callbacks.Plugin):
                 irc.error(str(e), Raise=True)
             try:
                 ircdb.users.setUser(user)
-            except ircdb.DuplicateHostmask:
+            except ircdb.DuplicateHostmask as e:
                 user.removeHostmask(hostmask)
-                irc.error(_('That hostmask is already registered.'),
-                          Raise=True)
+                if caller_is_owner:
+                    err = _('That hostmask is already registered to %s.') \
+                              % e.args[0]
+                else:
+                    err = _('That hostmask is already registered.')
+                irc.error(err, Raise=True)
             except ValueError as e:
                 irc.error(str(e), Raise=True)
             irc.replySuccess()
diff --git a/plugins/User/test.py b/plugins/User/test.py
index 85b0987d0..3dae049e9 100644
--- a/plugins/User/test.py
+++ b/plugins/User/test.py
@@ -40,6 +40,7 @@ class UserTestCase(PluginTestCase):
     plugins = ('User', 'Admin', 'Config')
     prefix1 = 'somethingElse!user@host1.tld'
     prefix2 = 'EvensomethingElse!user@host2.tld'
+    prefix3 = 'Completely!Different@host3.tld__no_testcap__'
 
     def testHostmaskList(self):
         self.assertError('hostmask list')
@@ -67,14 +68,36 @@ class UserTestCase(PluginTestCase):
         self.assertResponse('whoami', 'bar', frm=self.prefix2)
         self.assertNotError('hostmask add foo *!*@foobar/b',
                 frm=self.prefix1)
+
         self.assertResponse('hostmask add bar *!*@foobar/*',
-                'Error: That hostmask is already registered.',
+                'Error: That hostmask is already registered to foo.',
                 frm=self.prefix2)
         self.assertRegexp('hostmask list foo', '\*!\*@foobar/b',
                 frm=self.prefix1)
         self.assertNotRegexp('hostmask list bar', 'foobar',
                 frm=self.prefix2)
 
+    def testHostmaskOverlapPrivacy(self):
+        self.assertNotError('register foo passwd', frm=self.prefix1)
+        self.assertNotError('register bar passwd', frm=self.prefix3)
+        self.assertResponse('whoami', 'foo', frm=self.prefix1)
+        self.assertResponse('whoami', 'bar', frm=self.prefix3)
+        self.assertNotError('hostmask add foo *!*@foobar/b',
+                frm=self.prefix1)
+
+        ircdb.users.getUser('bar').addCapability('owner')
+        self.assertResponse('whoami', 'bar',
+                frm=self.prefix3)
+        self.assertResponse('capabilities', '[owner]',
+                frm=self.prefix3)
+        self.assertResponse('hostmask add *!*@foobar/*',
+                'Error: That hostmask is already registered to foo.',
+                frm=self.prefix3)
+        ircdb.users.getUser('bar').removeCapability('owner')
+        self.assertResponse('hostmask add *!*@foobar/*',
+                'Error: That hostmask is already registered.',
+                frm=self.prefix3)
+
 
     def testHostmask(self):
         self.assertResponse('hostmask', self.prefix)
diff --git a/src/ircdb.py b/src/ircdb.py
index 40d513384..f7c25dbe3 100644
--- a/src/ircdb.py
+++ b/src/ircdb.py
@@ -775,7 +775,7 @@ class UsersDictionary(utils.IterableMap):
         self.nextId = max(self.nextId, user.id)
         try:
             if self.getUserId(user.name) != user.id:
-                raise DuplicateHostmask(user.name)
+                raise DuplicateHostmask(user.name, user.name)
         except KeyError:
             pass
         for hostmask in user.hostmasks:
@@ -788,10 +788,10 @@ class UsersDictionary(utils.IterableMap):
                     # raise an exception.  So instead, we'll raise an
                     # exception, but be nice and give the offending hostmask
                     # back at the same time.
-                    raise DuplicateHostmask(hostmask)
+                    raise DuplicateHostmask(u.name, hostmask)
                 for otherHostmask in u.hostmasks:
                     if ircutils.hostmaskPatternEqual(hostmask, otherHostmask):
-                        raise DuplicateHostmask(hostmask)
+                        raise DuplicateHostmask(u.name, hostmask)
         self.invalidateCache(user.id)
         self.users[user.id] = user
         if flush: