diff --git a/tests/components/sensor/test_mqtt.py b/tests/components/sensor/test_mqtt.py
index b59ea867c58..8d1aef4d57f 100644
--- a/tests/components/sensor/test_mqtt.py
+++ b/tests/components/sensor/test_mqtt.py
@@ -39,3 +39,22 @@ class TestSensorMQTT(unittest.TestCase):
         self.assertEqual('100', state.state)
         self.assertEqual('fav unit',
                          state.attributes.get('unit_of_measurement'))
+
+    def test_setting_sensor_value_via_mqtt_json_message(self):
+        self.assertTrue(sensor.setup(self.hass, {
+            'sensor': {
+                'platform': 'mqtt',
+                'name': 'test',
+                'state_topic': 'test-topic',
+                'unit_of_measurement': 'fav unit',
+                'state_format': 'json:val'
+            }
+        }))
+
+        fire_mqtt_message(self.hass, 'test-topic', '{ "val": "100" }')
+        self.hass.pool.block_till_done()
+        state = self.hass.states.get('sensor.test')
+
+        self.assertEqual('100', state.state)
+        self.assertEqual('fav unit',
+                         state.attributes.get('unit_of_measurement'))