diff --git a/app/helpers/url_helper.rb b/app/helpers/url_helper.rb
index 6f623fcd..0f99a4a5 100644
--- a/app/helpers/url_helper.rb
+++ b/app/helpers/url_helper.rb
@@ -1,6 +1,6 @@
 module UrlHelper
   def govuk_url_for(path)
-    (Plek.website_root + path).to_s
+    Addressable::URI.join(Plek.website_root, path).to_s
   end
 
   def short_url_manger_url_for(path)
diff --git a/spec/helpers/url_helper_spec.rb b/spec/helpers/url_helper_spec.rb
index ac13311e..5fd37ef0 100644
--- a/spec/helpers/url_helper_spec.rb
+++ b/spec/helpers/url_helper_spec.rb
@@ -5,6 +5,10 @@
     it "should return a fully qualified gov.uk url from the given path" do
       expect(govuk_url_for("/some/path")).to eql "http://www.dev.gov.uk/some/path"
     end
+
+    it "should leave absolute URLs unchanged" do
+      expect(govuk_url_for("http://example.com/some/other/path")).to eql "http://example.com/some/other/path"
+    end
   end
 
   describe "short_url_manger_url_for" do