diff --git a/homeassistant/components/sensor/wunderground.py b/homeassistant/components/sensor/wunderground.py
index 69b53b0c259..7abc2a0fc1e 100644
--- a/homeassistant/components/sensor/wunderground.py
+++ b/homeassistant/components/sensor/wunderground.py
@@ -117,8 +117,11 @@ class WUndergroundSensor(Entity):
             else:
                 return self.rest.data[self._condition]
 
-        if self.rest.alerts and self._condition == 'alerts':
-            return len(self.rest.alerts)
+        if self._condition == 'alerts':
+            if self.rest.alerts:
+                return len(self.rest.alerts)
+            else:
+                return 0
         return STATE_UNKNOWN
 
     @property