diff --git a/Gemfile.lock b/Gemfile.lock
index 5f36b565a..25d9a1e29 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -123,10 +123,12 @@ GEM
     globalid (1.0.0)
       activesupport (>= 5.0)
     govuk_ab_testing (2.4.2)
-    govuk_app_config (4.8.0)
+    govuk_app_config (4.9.0)
       logstasher (~> 2.1)
+      plek (~> 4)
       prometheus_exporter (~> 2.0)
       puma (~> 5.6)
+      rack-proxy (~> 0.7)
       sentry-rails (~> 5.3)
       sentry-ruby (~> 5.3)
       statsd-ruby (~> 1.5)
@@ -234,6 +236,8 @@ GEM
       nio4r (~> 2.0)
     racc (1.6.0)
     rack (2.2.4)
+    rack-proxy (0.7.2)
+      rack
     rack-test (2.0.2)
       rack (>= 1.3)
     rack_strip_client_ip (0.0.2)