Net::HTTP.new produces SystemStackError?

http = Net::HTTP.new(HOST, PORT)

When I try to create a new Net::HTTP object, I get a SystemStackError:
“stack level too deep”. The trace shows a long list of
“/usr/lib/ruby/1.8/net/http.rb:333:in `newobj’”, which when I look at
the code seems to say that Net::HTTP keeps calling its own newobj method
recursively, with some Proxy object involved? I’m not fluent enough to
go digging around in the ruby Standard Library…

Same thing with Net::HTTP.start…

Any help?