diff --git a/Casks/firefox-nightly.rb b/Casks/firefox-nightly.rb
index 5dfdaf9f8..14ec0dcb6 100644
--- a/Casks/firefox-nightly.rb
+++ b/Casks/firefox-nightly.rb
@@ -2,6 +2,6 @@ class FirefoxNightly < Cask
   url 'http://ftp.mozilla.org/pub/mozilla.org/firefox/nightly/latest-trunk/firefox-31.0a1.en-US.mac.dmg'
   homepage 'http://nightly.mozilla.org/'
   version '31.0a1'
-  no_checksum
+  sha256 '1b252bb1c0f0fae1a8976395b6481534657ffbc05d91f111779755f55ec9e656'
   link 'FirefoxNightly.app'
 end