diff --git a/.travis.yml b/.travis.yml
index 9addadea..af2be34e 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -5,7 +5,7 @@ python:
     - 3.4
     - 3.3
 before_install:
-    - npm install -g less bower jupyter/configurable-http-proxy
+    - npm install -g less less-plugin-clean-css bower jupyter/configurable-http-proxy
     - git clone --quiet --depth 1 https://github.com/minrk/travis-wheels travis-wheels
 install:
     - pip install -f travis-wheels/wheelhouse -r dev-requirements.txt .
diff --git a/setup.py b/setup.py
index 5af9d9f2..7d90801e 100755
--- a/setup.py
+++ b/setup.py
@@ -158,7 +158,7 @@ class CSS(BaseCommand):
         sourcemap = style_css + '.map'
         try:
             check_call([
-                'lessc', '-x', '--verbose',
+                'lessc', '--clean-css', '--verbose',
                 '--source-map-basepath={}'.format(static),
                 '--source-map={}'.format(sourcemap),
                 '--source-map-rootpath=../',
@@ -166,7 +166,7 @@ class CSS(BaseCommand):
             ])
         except OSError as e:
             print("Failed to run lessc: %s" % e, file=sys.stderr)
-            print("You can install less with `npm install -g less`", file=sys.stderr)
+            print("You can install less with `npm install -g less less-plugin-clean-css`", file=sys.stderr)
             raise
         # update data-files in case this created new files
         self.distribution.data_files = get_data_files()