diff --git a/Library/Homebrew/tap_constants.rb b/Library/Homebrew/tap_constants.rb
index a9fc1bdd9b..670821f660 100644
--- a/Library/Homebrew/tap_constants.rb
+++ b/Library/Homebrew/tap_constants.rb
@@ -6,7 +6,7 @@ HOMEBREW_TAP_FORMULA_REGEX = T.let(%r{^([\w-]+)/([\w-]+)/([\w+-.@]+)$}, Regexp)
 # Match taps' casks, e.g. `someuser/sometap/somecask`
 HOMEBREW_TAP_CASK_REGEX = T.let(%r{^([\w-]+)/([\w-]+)/([a-z0-9\-_]+)$}, Regexp)
 # Match main cask taps' casks, e.g. `homebrew/cask/somecask` or `somecask`
-HOMEBREW_MAIN_TAP_CASK_REGEX = T.let(%r{^(?<tap>[Hh]omebrew/(?:homebrew-)?cask/)?(?<token>[a-z0-9\-_]+)$}, Regexp)
+HOMEBREW_MAIN_TAP_CASK_REGEX = T.let(%r{^(?:[Hh]omebrew/(?:homebrew-)?cask/)?(?<token>[a-z0-9\-_]+)$}, Regexp)
 # Match taps' directory paths, e.g. `HOMEBREW_LIBRARY/Taps/someuser/sometap`
 HOMEBREW_TAP_DIR_REGEX = T.let(
   %r{#{Regexp.escape(HOMEBREW_LIBRARY.to_s)}/Taps/(?<user>[\w-]+)/(?<repo>[\w-]+)}, Regexp