diff --git a/Gemfile b/Gemfile
index 16c28dcb9..29ecfca5e 100644
--- a/Gemfile
+++ b/Gemfile
@@ -16,7 +16,7 @@ gem "rails-controller-testing", "~> 1.0"
 gem "rails-i18n", ">= 4.0.4"
 gem "rails_translation_manager", "~> 0.1.0"
 gem "sass-rails", "~> 5.0"
-gem "slimmer", "~> 14.0"
+gem "slimmer", "~> 15.0"
 gem "uglifier", ">= 1.3.0"
 
 group :development, :test do
diff --git a/Gemfile.lock b/Gemfile.lock
index 656bdd47a..ba87a1f5e 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -290,7 +290,7 @@ GEM
       rubyzip (>= 1.2.2)
     sentry-raven (3.0.0)
       faraday (>= 1.0)
-    slimmer (14.0.0)
+    slimmer (15.0.0)
       activesupport
       json
       nokogiri (~> 1.7)
@@ -375,7 +375,7 @@ DEPENDENCIES
   rubocop-govuk (~> 3)
   sass-rails (~> 5.0)
   scss_lint-govuk (~> 0.2)
-  slimmer (~> 14.0)
+  slimmer (~> 15.0)
   uglifier (>= 1.3.0)
   webmock (~> 3.8.3)
   wraith (~> 4.2)