diff --git a/homeassistant/helpers/entity_component.py b/homeassistant/helpers/entity_component.py
index 44d0b8891d5..30d62608f9b 100644
--- a/homeassistant/helpers/entity_component.py
+++ b/homeassistant/helpers/entity_component.py
@@ -283,7 +283,7 @@ class EntityPlatform(object):
     def add_entities(self, new_entities, update_before_add=False):
         """Add entities for a single platform."""
         run_coroutine_threadsafe(
-            self.async_add_entities(new_entities, update_before_add),
+            self.async_add_entities(list(new_entities), update_before_add),
             self.component.hass.loop
         ).result()
 
diff --git a/tests/helpers/test_entity_component.py b/tests/helpers/test_entity_component.py
index 7c6b94963cf..02d8d36dafa 100644
--- a/tests/helpers/test_entity_component.py
+++ b/tests/helpers/test_entity_component.py
@@ -8,7 +8,7 @@ from unittest.mock import patch, Mock
 import homeassistant.core as ha
 import homeassistant.loader as loader
 from homeassistant.components import group
-from homeassistant.helpers.entity import Entity
+from homeassistant.helpers.entity import Entity, generate_entity_id
 from homeassistant.helpers.entity_component import EntityComponent
 from homeassistant.helpers import discovery
 import homeassistant.util.dt as dt_util
@@ -356,3 +356,20 @@ class TestHelpersEntityComponent(unittest.TestCase):
 
         assert sorted(self.hass.states.entity_ids()) == \
             ['test_domain.yummy_beer', 'test_domain.yummy_unnamed_device']
+
+    def test_adding_entities_with_generator_and_thread_callback(self):
+        """Test generator in add_entities that calls thread method.
+
+        We should make sure we resolve the generator to a list before passing
+        it into an async context.
+        """
+        component = EntityComponent(_LOGGER, DOMAIN, self.hass)
+
+        def create_entity(number):
+            """Create entity helper."""
+            entity = EntityTest()
+            entity.entity_id = generate_entity_id(component.entity_id_format,
+                                                  'Number', hass=self.hass)
+            return entity
+
+        component.add_entities(create_entity(i) for i in range(2))