diff --git a/Library/Homebrew/cask/cask_loader.rb b/Library/Homebrew/cask/cask_loader.rb
index 63d4f83367..cb6aefb10d 100644
--- a/Library/Homebrew/cask/cask_loader.rb
+++ b/Library/Homebrew/cask/cask_loader.rb
@@ -236,7 +236,7 @@ module Cask
       when 2..Float::INFINITY
         loaders = possible_tap_casks.map(&FromTapPathLoader.method(:new))
 
-        raise TapCaskAmbiguityError.new(ref, loaders) if loaders.map(&:tap).map(&:name).size == 1
+        raise TapCaskAmbiguityError.new(ref, loaders) if loaders.map(&:tap).map(&:name).uniq.size == 1
 
         return FromTapPathLoader.new(possible_tap_casks.first)
       end