diff --git a/lib/simplekit.rb b/lib/simplekit.rb
index 2af35510a2373025696cdbc550914ab7c8e3458a..e4ef4d23b16186275efefbcd3ae3334e0462400c 100644
--- a/lib/simplekit.rb
+++ b/lib/simplekit.rb
@@ -114,7 +114,7 @@ module SimpleKit
     def should_cancel?(event_notice)
       e = event_notice.event
       if @cancel_set.key? e
-        if @cancel_set[e] === nil
+        if @cancel_set[e].include? nil
           @cancel_set[e].delete nil
           @cancel_set.delete e if @cancel_set[e].empty?
           return true