diff --git a/homeassistant/components/http/view.py b/homeassistant/components/http/view.py
index 30d4ed0ab8d..c8f5d788dd2 100644
--- a/homeassistant/components/http/view.py
+++ b/homeassistant/components/http/view.py
@@ -45,8 +45,9 @@ class HomeAssistantView:
         """Return a JSON response."""
         try:
             msg = json.dumps(
-                result, sort_keys=True, cls=JSONEncoder).encode('UTF-8')
-        except TypeError as err:
+                result, sort_keys=True, cls=JSONEncoder, allow_nan=False
+            ).encode('UTF-8')
+        except (ValueError, TypeError) as err:
             _LOGGER.error('Unable to serialize to JSON: %s\n%s', err, result)
             raise HTTPInternalServerError
         response = web.Response(
diff --git a/homeassistant/components/websocket_api/http.py b/homeassistant/components/websocket_api/http.py
index 13be503a009..42c2c0a5751 100644
--- a/homeassistant/components/websocket_api/http.py
+++ b/homeassistant/components/websocket_api/http.py
@@ -13,11 +13,12 @@ from homeassistant.core import callback
 from homeassistant.components.http import HomeAssistantView
 from homeassistant.helpers.json import JSONEncoder
 
-from .const import MAX_PENDING_MSG, CANCELLATION_ERRORS, URL
+from .const import MAX_PENDING_MSG, CANCELLATION_ERRORS, URL, ERR_UNKNOWN_ERROR
 from .auth import AuthPhase, auth_required_message
 from .error import Disconnect
+from .messages import error_message
 
-JSON_DUMP = partial(json.dumps, cls=JSONEncoder)
+JSON_DUMP = partial(json.dumps, cls=JSONEncoder, allow_nan=False)
 
 
 class WebsocketAPIView(HomeAssistantView):
@@ -58,9 +59,12 @@ class WebSocketHandler:
                 self._logger.debug("Sending %s", message)
                 try:
                     await self.wsock.send_json(message, dumps=JSON_DUMP)
-                except TypeError as err:
+                except (ValueError, TypeError) as err:
                     self._logger.error('Unable to serialize to JSON: %s\n%s',
                                        err, message)
+                    await self.wsock.send_json(error_message(
+                        message['id'], ERR_UNKNOWN_ERROR,
+                        'Invalid JSON in response'))
 
     @callback
     def _send_message(self, message):
diff --git a/tests/components/http/test_view.py b/tests/components/http/test_view.py
index ac0e23edd64..ed97af9c764 100644
--- a/tests/components/http/test_view.py
+++ b/tests/components/http/test_view.py
@@ -10,6 +10,6 @@ async def test_invalid_json(caplog):
     view = HomeAssistantView()
 
     with pytest.raises(HTTPInternalServerError):
-        view.json(object)
+        view.json(float("NaN"))
 
-    assert str(object) in caplog.text
+    assert str(float("NaN")) in caplog.text
diff --git a/tests/components/websocket_api/test_commands.py b/tests/components/websocket_api/test_commands.py
index b83d4051356..dc9d0318fd1 100644
--- a/tests/components/websocket_api/test_commands.py
+++ b/tests/components/websocket_api/test_commands.py
@@ -300,3 +300,19 @@ async def test_states_filters_visible(hass, hass_admin_user, websocket_client):
 
     assert len(msg['result']) == 1
     assert msg['result'][0]['entity_id'] == 'test.entity'
+
+
+async def test_get_states_not_allows_nan(hass, websocket_client):
+    """Test get_states command not allows NaN floats."""
+    hass.states.async_set('greeting.hello', 'world', {
+        'hello': float("NaN")
+    })
+
+    await websocket_client.send_json({
+        'id': 5,
+        'type': commands.TYPE_GET_STATES,
+    })
+
+    msg = await websocket_client.receive_json()
+    assert not msg['success']
+    assert msg['error']['code'] == const.ERR_UNKNOWN_ERROR