diff --git a/Casks/firefoxnightly.rb b/Casks/firefox-nightly.rb
similarity index 96%
rename from Casks/firefoxnightly.rb
rename to Casks/firefox-nightly.rb
index 2ca100a52..8889af05e 100644
--- a/Casks/firefoxnightly.rb
+++ b/Casks/firefox-nightly.rb
@@ -1,4 +1,4 @@
-cask 'firefoxnightly' do
+cask 'firefox-nightly' do
   version '59.0a1'
   sha256 :no_check # required as upstream package is updated in-place