diff --git a/lib/minify.js b/lib/minify.js
index 8dd3e5aa..b7eb7341 100644
--- a/lib/minify.js
+++ b/lib/minify.js
@@ -54,6 +54,7 @@ function minify(files, options) {
                 cache: null,
                 eval: false,
                 ie8: false,
+                keep_classnames: false,
                 keep_fnames: false,
                 properties: false,
                 reserved: [],