diff --git a/Gemfile b/Gemfile
index 9389c0c..0c2ba3d 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,4 +1,5 @@
 source :rubygems
+ruby '1.9.3'
 
 gem 'nanoc'
 gem 'nanoc-cachebuster'