diff --git a/Gemfile b/Gemfile
index 8c1ceb7e7..419277678 100644
--- a/Gemfile
+++ b/Gemfile
@@ -4,4 +4,8 @@ source 'https://rubygems.org'
 gem 'jekyll', '~> 4.2.1'
 gem 'jekyll-redirect-from'
 
+# html-proofer checks for broken links.
+# used in docker-compose.yml test job
+gem 'html-proofer'
+
 gem "webrick", "~> 1.7"
diff --git a/docker-compose.yaml b/docker-compose.yaml
index be16897f9..c90b58cd4 100644
--- a/docker-compose.yaml
+++ b/docker-compose.yaml
@@ -43,7 +43,8 @@ services:
       command: /bin/bash -cl "
         bundle check
         && bundle exec jekyll doctor --source /srv/jekyll --destination /output
-        && bundle exec jekyll build --source /srv/jekyll --destination /output"
+        && bundle exec jekyll build --source /srv/jekyll --destination /output
+        && bundle exec htmlproofer --only_4xx --ignore-urls twitter.com /output"
 
    website:
      <<: *common