diff --git a/lib/cask/system_command.rb b/lib/cask/system_command.rb
index 285d9f8f35..4b31abb33a 100644
--- a/lib/cask/system_command.rb
+++ b/lib/cask/system_command.rb
@@ -70,7 +70,7 @@ class Cask::SystemCommand::Result
   end
 
   def plist
-    @plist ||= self.class._parse_plist(@command, @stdout)
+    @plist ||= self.class._parse_plist(@command, @stdout.dup)
   end
 
   def success?