diff --git a/README.md b/README.md
index 54d7f163..39509c56 100644
--- a/README.md
+++ b/README.md
@@ -2065,7 +2065,7 @@ Ubuntu:
     $ sudo apt-get install python-software-properties
     $ sudo apt-add-repository ppa:brightbox/ruby-ng
     $ sudo apt-get update
-    $ sudo apt-get install ruby2.1 ruby-switch
+    $ sudo apt-get install ruby2.1 ruby2.1-dev ruby-switch
     $ sudo ruby-switch --set ruby2.1
 
 Fedora: