Updating Ruby Gems

I was trying to update my RubyGems to 1.3.1 on OSX 10.5.5 to tryout the Merb Peepcode Screencast with the following command and got the resulting error:

$ sudo gem update --system
Updating RubyGems
Updating rubygems-update
Successfully installed rubygems-update-1.3.1
ERROR:  While executing gem ... (NameError)
    undefined local variable or method `remote_gemspecs' for #

So instead I tried the RubyGems update gem which worked:

$ sudo gem install rubygems-update
Successfully installed rubygems-update-1.3.1
1 gem installed
$ sudo update_rubygems