diff --git a/dockercoins/hasher/Dockerfile b/dockercoins/hasher/Dockerfile
index 62be9282..6313a131 100644
--- a/dockercoins/hasher/Dockerfile
+++ b/dockercoins/hasher/Dockerfile
@@ -1,6 +1,6 @@
 FROM ruby:alpine
 RUN apk add --update build-base curl
-RUN gem install sinatra
+RUN gem install sinatra --version '~> 3'
 RUN gem install thin
 ADD hasher.rb /
 CMD ["ruby", "hasher.rb"]