diff --git a/.travis.yml b/.travis.yml
index 76de489d9..a86ca9477 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,6 +1,6 @@
 language: ruby
 rvm:
-- 2.4.4
+- 2.5.3
 sudo: required
 dist: trusty
 
diff --git a/Dockerfile b/Dockerfile
index da37d574e..8b56879af 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -10,8 +10,8 @@ RUN usermod -a -G docker_env app
 # Use baseimage-docker's init process.
 CMD ["/sbin/my_init"]
 
-# Install Ruby 2.4.4
-RUN bash -lc 'rvm --default use ruby-2.4.4'
+# Install Ruby 2.5.3
+RUN bash -lc 'rvm --default use ruby-2.5.3'
 
 # Update installed APT packages
 RUN apt-get update && apt-get upgrade -y -o Dpkg::Options::="--force-confold" && \