diff --git a/lib/rackup/server.rb b/lib/rackup/server.rb
index 3304b87..33f6012 100644
--- a/lib/rackup/server.rb
+++ b/lib/rackup/server.rb
@@ -47,7 +47,7 @@ def parse!(args)
 
           opts.on("-I", "--include PATH",
                   "specify $LOAD_PATH (may be used more than once)") { |path|
-            (options[:include] ||= []).concat(path.split(":"))
+            (options[:include] ||= []).concat(path.split(::File::PATH_SEPARATOR))
           }
 
           opts.on("-r", "--require LIBRARY",