diff --git a/homeassistant/components/media_player/__init__.py b/homeassistant/components/media_player/__init__.py
index f98c6eeceaf..23261ea029e 100644
--- a/homeassistant/components/media_player/__init__.py
+++ b/homeassistant/components/media_player/__init__.py
@@ -307,7 +307,7 @@ async def async_setup(hass, config):
     )
     component.async_register_entity_service(
         SERVICE_JOIN,
-        {vol.Required(ATTR_GROUP_MEMBERS): list},
+        {vol.Required(ATTR_GROUP_MEMBERS): vol.All(cv.ensure_list, [cv.entity_id])},
         "async_join_players",
         [SUPPORT_GROUPING],
     )