diff --git a/lib/liquid/file_system.rb b/lib/liquid/file_system.rb
index 8e71f44..bf7ce1a 100644
--- a/lib/liquid/file_system.rb
+++ b/lib/liquid/file_system.rb
@@ -65,7 +65,7 @@ module Liquid
         File.join(root, @pattern % template_path)
       end
 
-      raise FileSystemError, "Illegal template path '#{File.expand_path(full_path)}'" unless File.expand_path(full_path) =~ /\A#{File.expand_path(root)}/
+      raise FileSystemError, "Illegal template path '#{File.expand_path(full_path)}'" unless File.expand_path(full_path).start_with?(File.expand_path(root))
 
       full_path
     end