diff --git a/README.md b/README.md
index 6b8e4b6..c3b9791 100644
--- a/README.md
+++ b/README.md
@@ -161,6 +161,10 @@ Default value: Defaults to `options.width/options.height` if both are provided,
 Type: `Integer`
 Default value: `3`
 
+#### options['cleanCss']
+Type: `Boolean`
+Default value: `true` If `true`, CSS is cleaned with clean-css merging selectors and properties.
+
 ## Contributing
 
 In lieu of a formal styleguide, take care to maintain the existing coding style. Add unit tests for any new or changed functionality. Lint and test your code using Grunt.