diff --git a/Dockerfile b/Dockerfile
index 1b49e3b..9efcb9b 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -31,7 +31,7 @@ COPY --chown=app:www-data ./.git/ ./.git/
 RUN git archive -o ../web.tar.gz HEAD
 
 FROM lunar/monit:3.9
-RUN apk add --no-cache libxslt libxml2 tzdata ruby ruby-json ruby-bigdecimal ruby-rake
+RUN apk add --no-cache libxslt libxml2 tzdata ruby ruby-json ruby-bigdecimal ruby-rake ruby-etc
 RUN apk add --no-cache sqlite-libs
 RUN apk add --no-cache darkhttpd
 RUN gem install --no-user-install --no-ri --no-rdoc bundler