--- a/test/test_image_size.rb
+++ b/test/test_image_size.rb
@@ -1,4 +1,4 @@
-require File.dirname(__FILE__) + '/test_helper.rb'
+require File.expand_path(File.join(File.dirname(__FILE__), 'test_helper'))
 
 class TestImageSize < Test::Unit::TestCase
 
