diff --git a/mopidy/core/mixer.py b/mopidy/core/mixer.py
index 1f5ada9e..3388d706 100644
--- a/mopidy/core/mixer.py
+++ b/mopidy/core/mixer.py
@@ -25,10 +25,11 @@ class MixerController(object):
     def set_volume(self, volume):
         """Set the volume.
 
-        The volume is defined as an integer in range [0..100] or :class:`None`
-        if the mixer is disabled.
+        The volume is defined as an integer in range [0..100].
 
         The volume scale is linear.
+
+        Returns :class:`True` if call is successful, otherwise :class:`False`.
         """
         if self._mixer is None:
             return False
@@ -41,9 +42,7 @@ class MixerController(object):
         :class:`True` if muted, :class:`False` unmuted, :class:`None` if
         unknown.
         """
-        if self._mixer is None:
-            return False
-        else:
+        if self._mixer is not None:
             return self._mixer.get_mute().get()
 
     def set_mute(self, mute):
diff --git a/mopidy/mpd/protocol/audio_output.py b/mopidy/mpd/protocol/audio_output.py
index 6ffedcf1..565ea3d0 100644
--- a/mopidy/mpd/protocol/audio_output.py
+++ b/mopidy/mpd/protocol/audio_output.py
@@ -14,7 +14,7 @@ def disableoutput(context, outputid):
     """
     if outputid == 0:
         success = context.core.mixer.set_mute(False).get()
-        if success is False:
+        if not success:
             raise exceptions.MpdSystemError('problems disabling output')
     else:
         raise exceptions.MpdNoExistError('No such audio output')
@@ -31,7 +31,7 @@ def enableoutput(context, outputid):
     """
     if outputid == 0:
         success = context.core.mixer.set_mute(True).get()
-        if success is False:
+        if not success:
             raise exceptions.MpdSystemError('problems enabling output')
     else:
         raise exceptions.MpdNoExistError('No such audio output')
@@ -49,7 +49,7 @@ def toggleoutput(context, outputid):
     if outputid == 0:
         mute_status = context.core.mixer.get_mute().get()
         success = context.core.mixer.set_mute(not mute_status)
-        if success is False:
+        if not success:
             raise exceptions.MpdSystemError('problems toggling output')
     else:
         raise exceptions.MpdNoExistError('No such audio output')
diff --git a/mopidy/mpd/protocol/playback.py b/mopidy/mpd/protocol/playback.py
index 4cf8b2e8..86f2e36b 100644
--- a/mopidy/mpd/protocol/playback.py
+++ b/mopidy/mpd/protocol/playback.py
@@ -397,7 +397,7 @@ def setvol(context, volume):
     # NOTE: we use INT as clients can pass in +N etc.
     value = min(max(0, volume), 100)
     success = context.core.mixer.set_volume(value).get()
-    if success is False:
+    if not success:
         raise exceptions.MpdSystemError('problems setting volume')
 
 
diff --git a/tests/core/test_mixer.py b/tests/core/test_mixer.py
index 6485f3e8..c4126eaa 100644
--- a/tests/core/test_mixer.py
+++ b/tests/core/test_mixer.py
@@ -42,17 +42,17 @@ class CoreNoneMixerTest(unittest.TestCase):
     def setUp(self):  # noqa: N802
         self.core = core.Core(mixer=None, backends=[])
 
-    def test_get_volume_return_none(self):
+    def test_get_volume_return_none_because_it_is_unknown(self):
         self.assertEqual(self.core.mixer.get_volume(), None)
 
-    def test_set_volume_return_false(self):
+    def test_set_volume_return_false_because_it_failed(self):
         self.assertEqual(self.core.mixer.set_volume(30), False)
 
-    def test_get_set_mute_return_proper_state(self):
-        self.assertEqual(self.core.mixer.set_mute(False), False)
-        self.assertEqual(self.core.mixer.get_mute(), False)
+    def test_get_mute_return_none_because_it_is_unknown(self):
+        self.assertEqual(self.core.mixer.get_mute(), None)
+
+    def test_set_mute_return_false_because_it_failed(self):
         self.assertEqual(self.core.mixer.set_mute(True), False)
-        self.assertEqual(self.core.mixer.get_mute(), False)
 
 
 @mock.patch.object(mixer.MixerListener, 'send')
diff --git a/tests/mpd/protocol/test_audio_output.py b/tests/mpd/protocol/test_audio_output.py
index 322bf181..b42b4c56 100644
--- a/tests/mpd/protocol/test_audio_output.py
+++ b/tests/mpd/protocol/test_audio_output.py
@@ -90,20 +90,22 @@ class AudioOutputHandlerNoneMixerTest(protocol.BaseTestCase):
     enable_mixer = False
 
     def test_enableoutput(self):
-        self.core.mixer.set_mute(False)
+        self.assertEqual(self.core.mixer.get_mute().get(), None)
 
         self.send_request('enableoutput "0"')
         self.assertInResponse(
             'ACK [52@0] {enableoutput} problems enabling output')
-        self.assertEqual(self.core.mixer.get_mute().get(), False)
+
+        self.assertEqual(self.core.mixer.get_mute().get(), None)
 
     def test_disableoutput(self):
-        self.core.mixer.set_mute(True)
+        self.assertEqual(self.core.mixer.get_mute().get(), None)
 
         self.send_request('disableoutput "0"')
         self.assertInResponse(
             'ACK [52@0] {disableoutput} problems disabling output')
-        self.assertEqual(self.core.mixer.get_mute().get(), False)
+
+        self.assertEqual(self.core.mixer.get_mute().get(), None)
 
     def test_outputs_when_unmuted(self):
         self.core.mixer.set_mute(False)