diff --git a/plan.inc.php b/plan.inc.php
index 16a30c2..c8cb692 100644
--- a/plan.inc.php
+++ b/plan.inc.php
@@ -246,7 +246,8 @@ class Plan
   {
     return Amp\call(function() use($task) {
 
-      yield $this->_startAsync($task);
+      if(!yield $this->_startAsync($task))
+        return;
 
       while(!$this->isOver())
       {
@@ -333,7 +334,7 @@ class Plan
     });
   }
 
-  function _ignoreDevice($device, $reason)
+  function _ignoreDevice(string $device, string $reason)
   {
     $this->session->ignoreDevice($device, $reason);