diff --git a/Library/Homebrew/cask/cask.rb b/Library/Homebrew/cask/cask.rb
index 12d578df81..f279630487 100644
--- a/Library/Homebrew/cask/cask.rb
+++ b/Library/Homebrew/cask/cask.rb
@@ -133,7 +133,7 @@ module Cask
         end,
         "caveats"        => caveats,
         "depends_on"     => depends_on,
-        "conflicts_with" => conflicts_with.to_a,
+        "conflicts_with" => conflicts_with.to_h,
         "container"      => container,
         "auto_updates"   => auto_updates,
       }
diff --git a/Library/Homebrew/cask/dsl/conflicts_with.rb b/Library/Homebrew/cask/dsl/conflicts_with.rb
index 75242b9490..e9db95fd27 100644
--- a/Library/Homebrew/cask/dsl/conflicts_with.rb
+++ b/Library/Homebrew/cask/dsl/conflicts_with.rb
@@ -26,10 +26,8 @@ module Cask
         end
       end
 
-      def to_a
-        conflicts={}
-        @pairs.each { |k, v| conflicts[k]=v }
-        conflicts
+      def to_h
+        Hash[VALID_KEYS.map { |key| [key, instance_variable_get("@#{key}").to_a] }]
       end
     end
   end