diff --git a/Rakefile b/Rakefile
index 712dcad..3151585 100644
--- a/Rakefile
+++ b/Rakefile
@@ -37,7 +37,7 @@ hoe = Hoe.spec 'pkcs11' do
   spec_extras[:has_rdoc] = 'yard'
 end
 
-ENV['RUBY_CC_VERSION'] = '1.8.6:1.9.2'
+ENV['RUBY_CC_VERSION'] ||= '1.8.6:1.9.2'
 
 Rake::ExtensionTask.new('pkcs11_ext', hoe.spec) do |ext|
   ext.ext_dir = 'ext'