diff --git a/mopidy/mpd/protocol/__init__.py b/mopidy/mpd/protocol/__init__.py
index 3c501bbb..f0ae814b 100644
--- a/mopidy/mpd/protocol/__init__.py
+++ b/mopidy/mpd/protocol/__init__.py
@@ -138,7 +138,13 @@ class Commands(object):
             def validate(*args, **kwargs):
                 if varargs:
                     return func(*args, **kwargs)
-                callargs = inspect.getcallargs(func, *args, **kwargs)
+
+                try:
+                    callargs = inspect.getcallargs(func, *args, **kwargs)
+                except TypeError:
+                    raise exceptions.MpdArgError(
+                        'wrong number of arguments for "%s"' % name)
+
                 for key, value in callargs.items():
                     default = defaults.get(key, object())
                     if key in validators and value != default:
@@ -146,6 +152,7 @@ class Commands(object):
                             callargs[key] = validators[key](value)
                         except ValueError:
                             raise exceptions.MpdArgError('incorrect arguments')
+
                 return func(**callargs)
 
             validate.auth_required = auth_required
diff --git a/tests/mpd/protocol/test_authentication.py b/tests/mpd/protocol/test_authentication.py
index 6a39ba81..4937c04f 100644
--- a/tests/mpd/protocol/test_authentication.py
+++ b/tests/mpd/protocol/test_authentication.py
@@ -19,6 +19,12 @@ class AuthenticationActiveTest(protocol.BaseTestCase):
         self.assertFalse(self.dispatcher.authenticated)
         self.assertEqualResponse('ACK [3@0] {password} incorrect password')
 
+    def test_authentication_without_password_fails(self):
+        self.sendRequest('password')
+        self.assertFalse(self.dispatcher.authenticated)
+        self.assertEqualResponse(
+            'ACK [2@0] {password} wrong number of arguments for "password"')
+
     def test_anything_when_not_authenticated_should_fail(self):
         self.sendRequest('any request at all')
         self.assertFalse(self.dispatcher.authenticated)
diff --git a/tests/mpd/test_commands.py b/tests/mpd/test_commands.py
index bb4effb8..2b4205fe 100644
--- a/tests/mpd/test_commands.py
+++ b/tests/mpd/test_commands.py
@@ -169,15 +169,15 @@ class TestCommands(unittest.TestCase):
 
     def test_call_incorrect_args(self):
         self.commands.add('foo')(lambda context: context)
-        with self.assertRaises(TypeError):
+        with self.assertRaises(exceptions.MpdArgError):
             self.commands.call(['foo', 'bar'])
 
         self.commands.add('bar')(lambda context, required: context)
-        with self.assertRaises(TypeError):
+        with self.assertRaises(exceptions.MpdArgError):
             self.commands.call(['bar', 'bar', 'baz'])
 
         self.commands.add('baz')(lambda context, optional=None: context)
-        with self.assertRaises(TypeError):
+        with self.assertRaises(exceptions.MpdArgError):
             self.commands.call(['baz', 'bar', 'baz'])
 
     def test_validator_gets_applied_to_required_arg(self):