diff --git a/homeassistant/components/media_player/sonos.py b/homeassistant/components/media_player/sonos.py
index c675210a075..38408914448 100644
--- a/homeassistant/components/media_player/sonos.py
+++ b/homeassistant/components/media_player/sonos.py
@@ -71,7 +71,7 @@ PLATFORM_SCHEMA = PLATFORM_SCHEMA.extend({
 })
 
 SONOS_SCHEMA = vol.Schema({
-    ATTR_ENTITY_ID: cv.entity_ids,
+    vol.Optional(ATTR_ENTITY_ID): cv.entity_ids,
 })
 
 SONOS_JOIN_SCHEMA = SONOS_SCHEMA.extend({
@@ -923,17 +923,22 @@ class SonosDevice(MediaPlayerDevice):
 
     def join(self, master):
         """Join the player to a group."""
-        coord = [device.soco_device for device in self.hass.data[DATA_SONOS]
+        coord = [device for device in self.hass.data[DATA_SONOS]
                  if device.entity_id == master]
 
         if coord and master != self.entity_id:
-            self._player.join(coord[0])
+            coord = coord[0]
+            if coord.soco_device.group.coordinator != coord.soco_device:
+                coord.soco_device.unjoin()
+            self._player.join(coord.soco_device)
+            self._coordinator = coord
         else:
             _LOGGER.error("Master not found %s", master)
 
     def unjoin(self):
         """Unjoin the player from a group."""
         self._player.unjoin()
+        self._coordinator = None
 
     def snapshot(self, with_group=True):
         """Snapshot the player."""
diff --git a/tests/components/media_player/test_sonos.py b/tests/components/media_player/test_sonos.py
index e494d3242fa..3d80536fb82 100644
--- a/tests/components/media_player/test_sonos.py
+++ b/tests/components/media_player/test_sonos.py
@@ -251,7 +251,7 @@ class TestSonosMediaPlayer(unittest.TestCase):
 
         device_master = mock.MagicMock()
         device_master.entity_id = "media_player.test"
-        device_master.soco_device = device
+        device_master.soco_device = mock.MagicMock()
         self.hass.data[sonos.DATA_SONOS].append(device_master)
 
         join_mock.return_value = True