diff --git a/mopidy/mpd/protocol/__init__.py b/mopidy/mpd/protocol/__init__.py
index c86a39e6..1be42dcc 100644
--- a/mopidy/mpd/protocol/__init__.py
+++ b/mopidy/mpd/protocol/__init__.py
@@ -14,6 +14,8 @@ from __future__ import unicode_literals
 
 import inspect
 
+from mopidy.mpd import exceptions
+
 #: The MPD protocol uses UTF-8 for encoding all data.
 ENCODING = 'UTF-8'
 
@@ -79,7 +81,7 @@ class Commands(object):
     def add(self, name, auth_required=True, list_command=True, **validators):
         def wrapper(func):
             if name in self.handlers:
-                raise Exception('%s already registered' % name)
+                raise ValueError('%s already registered' % name)
 
             args, varargs, keywords, defaults = inspect.getargspec(func)
             defaults = dict(zip(args[-len(defaults or []):], defaults or []))
@@ -104,7 +106,10 @@ class Commands(object):
                 for key, value in callargs.items():
                     default = defaults.get(key, object())
                     if key in validators and value != default:
-                        callargs[key] = validators[key](value)
+                        try:
+                            callargs[key] = validators[key](value)
+                        except ValueError:
+                            raise exceptions.MpdArgError('incorrect arguments')
                 return func(**callargs)
 
             validate.auth_required = auth_required
@@ -114,11 +119,10 @@ class Commands(object):
         return wrapper
 
     def call(self, args, context=None):
-        # TODO: raise mopidy.mpd.exceptions
         if not args:
-            raise TypeError('No args provided')
+            raise exceptions.MpdNoCommand()
         if args[0] not in self.handlers:
-            raise LookupError('Unknown command')
+            raise exceptions.MpdUnknownCommand(command=args[0])
         return self.handlers[args[0]](context, *args[1:])
 
 
diff --git a/tests/mpd/test_commands.py b/tests/mpd/test_commands.py
index 845796af..91a9125a 100644
--- a/tests/mpd/test_commands.py
+++ b/tests/mpd/test_commands.py
@@ -4,7 +4,7 @@ from __future__ import unicode_literals
 
 import unittest
 
-from mopidy.mpd import protocol
+from mopidy.mpd import exceptions, protocol
 
 
 class TestConverts(unittest.TestCase):
@@ -134,7 +134,7 @@ class TestCommands(unittest.TestCase):
         self.assertEqual(sentinel3, self.commands.call(['baz']))
 
     def test_call_with_nonexistent_handler(self):
-        with self.assertRaises(LookupError):
+        with self.assertRaises(exceptions.MpdUnknownCommand):
             self.commands.call(['bar'])
 
     def test_call_passes_context(self):
@@ -144,7 +144,7 @@ class TestCommands(unittest.TestCase):
             sentinel, self.commands.call(['foo'], context=sentinel))
 
     def test_call_without_args_fails(self):
-        with self.assertRaises(TypeError):
+        with self.assertRaises(exceptions.MpdNoCommand):
             self.commands.call([])
 
     def test_call_passes_required_argument(self):
@@ -212,6 +212,16 @@ class TestCommands(unittest.TestCase):
             func = lambda context: True
             self.commands.add('bar', context=lambda v: v)(func)
 
+    def test_validator_value_error_is_converted(self):
+        def validdate(value):
+            raise ValueError
+
+        func = lambda context, arg: True
+        self.commands.add('bar', arg=validdate)(func)
+
+        with self.assertRaises(exceptions.MpdArgError):
+            self.commands.call(['bar', 'test'])
+
     def test_auth_required_gets_stored(self):
         func1 = lambda context: context
         func2 = lambda context: context