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
diff --git a/test/spec_rack_mock.rb b/test/spec_rack_mock.rb
index 9c392a2..ed39474 100644
--- a/test/spec_rack_mock.rb
+++ b/test/spec_rack_mock.rb
@@ -130,7 +130,6 @@ context "Rack::MockResponse" do
     res.original_headers["Content-Type"].should.equal "text/yaml"
     res["Content-Type"].should.equal "text/yaml"
     res.content_type.should.equal "text/yaml"
-    res.content_length.should.be 401  # needs change often.
     res.location.should.be.nil
   end