diff --git a/mopidy/config/types.py b/mopidy/config/types.py
index c43da740..92ccb89a 100644
--- a/mopidy/config/types.py
+++ b/mopidy/config/types.py
@@ -184,19 +184,22 @@ class LogLevel(ConfigValue):
     with any casing.
     """
     levels = {
-        'critical': logging.CRITICAL,
-        'error': logging.ERROR,
-        'warning': logging.WARNING,
-        'info': logging.INFO,
-        'debug': logging.DEBUG,
+        b'critical': logging.CRITICAL,
+        b'error': logging.ERROR,
+        b'warning': logging.WARNING,
+        b'info': logging.INFO,
+        b'debug': logging.DEBUG,
     }
 
     def deserialize(self, value):
         validators.validate_choice(value.lower(), self.levels.keys())
         return self.levels.get(value.lower())
 
-    def serialize(self, value):
-        return dict((v, k) for k, v in self.levels.items()).get(value)
+    def serialize(self, value, display=False):
+        lookup = dict((v, k) for k, v in self.levels.items())
+        if value in lookup:
+            return lookup[value]
+        return b''
 
 
 class Hostname(ConfigValue):
diff --git a/tests/config/types_test.py b/tests/config/types_test.py
index a5f2c9dc..e8b026d3 100644
--- a/tests/config/types_test.py
+++ b/tests/config/types_test.py
@@ -261,7 +261,7 @@ class LogLevelTest(unittest.TestCase):
         value = types.LogLevel()
         for name, level in self.levels.items():
             self.assertEqual(name, value.serialize(level))
-        self.assertIsNone(value.serialize(1337))
+        self.assertEqual(b'', value.serialize(1337))
 
 
 class HostnameTest(unittest.TestCase):