diff --git a/lib/rack/rewindable_input.rb b/lib/rack/rewindable_input.rb
index accd96b..d71fde6 100644
--- a/lib/rack/rewindable_input.rb
+++ b/lib/rack/rewindable_input.rb
@@ -94,7 +94,7 @@ module Rack
     end
     
     def filesystem_has_posix_semantics?
-      RUBY_PLATFORM !~ /(mswin|mingw|cygwin|java)/
+      RUBY_PLATFORM !~ /(mswin|mingw|cygwin|java)/ && RUBY_VERSION < '1.9.1'
     end
   end
 end
