diff --git a/src/calibre/srv/standalone.py b/src/calibre/srv/standalone.py
index c5f56deabf..429b626314 100644
--- a/src/calibre/srv/standalone.py
+++ b/src/calibre/srv/standalone.py
@@ -184,7 +184,9 @@ def manage_users(path=None):
             m.set_readonly(username, not readonly)
 
     def change_restriction(username):
-        r = m.restrictions(username) or {}
+        r = m.restrictions(username)
+        if r is None:
+            raise SystemExit('The user {} does not exist'.format(username))
         if r['allowed_library_names']:
             prints(_('{} is currently only allowed to access the libraries named: {}').format(
                 username, ', '.join(r['allowed_library_names'])))
diff --git a/src/calibre/srv/tests/auth.py b/src/calibre/srv/tests/auth.py
index ba459513f9..8fde82c62b 100644
--- a/src/calibre/srv/tests/auth.py
+++ b/src/calibre/srv/tests/auth.py
@@ -153,6 +153,7 @@ class TestAuth(BaseTest):
             self.assertEqual(library_info('a')[0], {'l%d'%i:'l%d'%i for i in range(1, 4) if i == 3})
             self.assertEqual(library_info('a')[1], 'l3')
             self.assertRaises(HTTPForbidden, get_library, 'a', 'l1')
+            self.assertRaises(HTTPForbidden, get_library, 'xxx')
 
     # }}}
 
diff --git a/src/calibre/srv/users.py b/src/calibre/srv/users.py
index b84c4f36f5..2c41f78624 100644
--- a/src/calibre/srv/users.py
+++ b/src/calibre/srv/users.py
@@ -197,7 +197,6 @@ class UserManager(object):
         with self.lock:
             r = self._restrictions.get(username)
             if r is None:
-                r = self._restrictions[username] = parse_restriction('{}')
                 for restriction, in self.conn.cursor().execute(
                         'SELECT restriction FROM users WHERE name=?', (username,)):
                     self._restrictions[username] = r = parse_restriction(restriction)