diff --git a/.ruby-version b/.ruby-version
index 005119ba..ecd7ee50 100644
--- a/.ruby-version
+++ b/.ruby-version
@@ -1 +1 @@
-2.4.1
+2.5.8
diff --git a/docs/setting-up-your-environment.md b/docs/setting-up-your-environment.md
index 8071bc17..11880fdb 100644
--- a/docs/setting-up-your-environment.md
+++ b/docs/setting-up-your-environment.md
@@ -42,19 +42,19 @@ following command:
 
     source ~/.rvm/scripts/rvm
 
-**Install Ruby 2.4.1**
+**Install Ruby 2.5.8**
 
-To install Ruby 2.4.1, simply run this command:
+To install Ruby 2.5.8, simply run this command:
 
-    rvm install 2.4.1
+    rvm install 2.5.8
 
 Sometimes this will find a pre-compiled Ruby package for your Linux
 distribution, but sometimes it will need to compile Ruby from scratch
 (which takes about 15 minutes).
 
-After Ruby 2.4.1 is installed, make it your default Ruby:
+After Ruby 2.5.8 is installed, make it your default Ruby:
 
-    rvm alias create default ruby-2.4.1
+    rvm alias create default ruby-2.5.8
 
 And tell your system to use it: