diff --git a/homeassistant/components/script.py b/homeassistant/components/script.py
index 59b55a1289b..dbb145ebb1d 100644
--- a/homeassistant/components/script.py
+++ b/homeassistant/components/script.py
@@ -70,8 +70,12 @@ def setup(hass, config):
         """ Execute a service call to script.<script name>. """
         entity_id = ENTITY_ID_FORMAT.format(service.service)
         script = component.entities.get(entity_id)
-        if script:
-            script.turn_on()
+        if not script:
+            return
+        if script.is_on:
+            _LOGGER.warning("Script %s already running.", entity_id)
+            return
+        script.turn_on()
 
     for object_id, cfg in config[DOMAIN].items():
         if object_id != slugify(object_id):
diff --git a/tests/components/test_script.py b/tests/components/test_script.py
index 30b7e4e3c8f..3d2c7512ae2 100644
--- a/tests/components/test_script.py
+++ b/tests/components/test_script.py
@@ -232,3 +232,40 @@ class TestScript(unittest.TestCase):
         self.assertFalse(script.is_on(self.hass, ENTITY_ID))
 
         self.assertEqual(0, len(calls))
+
+    def test_turn_on_service(self):
+        """
+        Verifies that the turn_on service for a script only turns on scripts
+        that are not currently running.
+        """
+        event = 'test_event'
+        calls = []
+
+        def record_event(event):
+            calls.append(event)
+
+        self.hass.bus.listen(event, record_event)
+
+        self.assertTrue(script.setup(self.hass, {
+            'script': {
+                'test': {
+                    'sequence': [{
+                        'delay': {
+                            'seconds': 5
+                        }
+                    }, {
+                        'event': event,
+                    }]
+                }
+            }
+        }))
+
+        script.turn_on(self.hass, ENTITY_ID)
+        self.hass.pool.block_till_done()
+        self.assertTrue(script.is_on(self.hass, ENTITY_ID))
+        self.assertEqual(0, len(calls))
+
+        # calling turn_on a second time should not advance the script
+        script.turn_on(self.hass, ENTITY_ID)
+        self.hass.pool.block_till_done()
+        self.assertEqual(0, len(calls))