diff --git a/Gemfile b/Gemfile
index a0cb5c222..5c3af149f 100644
--- a/Gemfile
+++ b/Gemfile
@@ -13,4 +13,4 @@ gem 'coderay', '1.1.3'
 gem 'pygments.rb', '1.2.1'
 gem 'thread_safe', '0.3.6'
 gem 'epubcheck-ruby', '4.2.4.0'
-gem 'html-proofer', '3.17.3'
+gem 'html-proofer', '3.18.1'