diff --git a/Changelog.md b/Changelog.md
--- a/Changelog.md
+++ b/Changelog.md
@@ -1,3 +1,7 @@
+## 1.2.12
+
+* Increased the upper-bound of `async` to allow < 2.2.
+
 ## 1.2.11
 
 * Increased the upper-bound of aeson to allow < 0.11.
diff --git a/engine-io.cabal b/engine-io.cabal
--- a/engine-io.cabal
+++ b/engine-io.cabal
@@ -1,5 +1,5 @@
 name: engine-io
-version: 1.2.11
+version: 1.2.12
 synopsis: A Haskell implementation of Engine.IO
 homepage: http://github.com/ocharles/engine.io
 license: BSD3
@@ -28,7 +28,7 @@
 
   build-depends:
     aeson >=0.7 && <0.11,
-    async >=2.0 && <2.1,
+    async >=2.0 && <2.2,
     attoparsec >=0.11 && <0.14,
     base >=4.6 && <4.9,
     base64-bytestring >=1.0 && <1.1,