--- a/support/file_map.rb
+++ b/support/file_map.rb
@@ -1,6 +1,6 @@
 module FileMap
 
-  GIT_FILES      = `git ls-files`.split("\n")
+  GIT_FILES      = Dir['lib/**/*']
   ALL_LIB_FILES  = Dir['lib/concurrent/**/*.rb'] & GIT_FILES
   EDGE_LIB_FILES = Dir['lib/concurrent/actor.rb',
                        'lib/concurrent/actor/**/*.rb',