diff --git a/Gemfile b/Gemfile
index 7d84ca16..f6b70217 100644
--- a/Gemfile
+++ b/Gemfile
@@ -29,5 +29,5 @@ end
 ## you can put whatever you want here and bundler will tell us humans to
 ## install the new Gems.
 group :slow_test do
-  gem 'html-proofer', '2.1.0'
+  gem 'html-proofer', '3.6.0'
 end