diff --git a/Dockerfile b/Dockerfile
index f8d1aec4..892cfe91 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -13,6 +13,9 @@ RUN apt-get update -qq && apt-get install -y --no-install-recommends \
 
 WORKDIR /app
 
+# Install correct bundler version (must match Gemfile.lock BUNDLED WITH)
+RUN gem install bundler:2.4.21
+
 # Install gems
 COPY Gemfile Gemfile.lock ./
 RUN bundle install --deployment --without development test --jobs 4