diff --git a/builder.Dockerfile b/builder.Dockerfile
index 846dc1c..3418ad0 100644
--- a/builder.Dockerfile
+++ b/builder.Dockerfile
@@ -1,7 +1,9 @@
 ARG RUBY_MAJOR
 FROM ghcr.io/alphagov/govuk-ruby-base:${RUBY_MAJOR}
 
-RUN install_packages g++ libc-dev libssl-dev make git gpg libmariadb-dev-compat libpq-dev xz-utils
+RUN install_packages \
+    g++ libc-dev libssl-dev make git gpg libmariadb-dev-compat libpq-dev \
+    libyaml-dev xz-utils
 
 # Environment variables to make build cleaner and faster
 ENV BUNDLE_IGNORE_MESSAGES=1 \