diff --git a/Gemfile.lock b/Gemfile.lock
index 2d629a240d3..7583e4722b3 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -5,7 +5,7 @@ GEM
     addressable (2.8.7)
       public_suffix (>= 2.0.2, < 7.0)
     afm (0.2.2)
-    async (2.20.0)
+    async (2.21.0)
       console (~> 1.29)
       fiber-annotation
       io-event (~> 1.6, >= 1.6.5)