diff --git a/lib/ruby/java/classpath.rb b/lib/ruby/java/classpath.rb
index 4fc257aa..6f1f0e88 100644
--- a/lib/ruby/java/classpath.rb
+++ b/lib/ruby/java/classpath.rb
@@ -2,6 +2,7 @@ module Java
 
   class Classpath
     require 'pathname'
+    require 'rbconfig'
 
     def initialize(root_dir)
       @root = root_dir
@@ -20,7 +21,7 @@ def definition
     end
 
     def separator
-     PLATFORM['win32'] ? ";" : ":"
+     Config::CONFIG['host_os'] =~ /mswin|mingw/ ? ';' : ':'
     end
 
   end