diff --git a/docs/rails.md b/docs/rails.md
index 0a164ca75..105f0f45e 100644
--- a/docs/rails.md
+++ b/docs/rails.md
@@ -26,6 +26,7 @@ Dockerfile consists of:
     RUN mkdir /myapp
     WORKDIR /myapp
     ADD Gemfile /myapp/Gemfile
+    ADD Gemfile.lock /myapp/Gemfile.lock
     RUN bundle install
     ADD . /myapp