diff --git a/homeassistant/components/sensor/filter.py b/homeassistant/components/sensor/filter.py
index aad7fec26a0..3faf51a5f47 100644
--- a/homeassistant/components/sensor/filter.py
+++ b/homeassistant/components/sensor/filter.py
@@ -74,7 +74,7 @@ FILTER_TIME_SMA_SCHEMA = FILTER_SCHEMA.extend({
     vol.Required(CONF_FILTER_NAME): FILTER_NAME_TIME_SMA,
     vol.Optional(CONF_TIME_SMA_TYPE,
                  default=TIME_SMA_LAST): vol.In(
-                     [None, TIME_SMA_LAST]),
+                     [TIME_SMA_LAST]),
 
     vol.Required(CONF_FILTER_WINDOW_SIZE): vol.All(cv.time_period,
                                                    cv.positive_timedelta)