Uninitialized Constant Rake::DSL and Heroku

I took @jqr's advice and signed up for Heroku this morning. Agile Web Development had me working on running a virtual name server with Apache and it was way too complicated for my tastes. Apparently coders who don't want to deal with server-side headaches are pretty common, hence Heroku!

But I've hit a snag. I get an uninitialized constant Rake::DSL error whenever I try to run a migration on Heroku. Here's the full error:

gozer /users/tylermoore/code/depot master$ heroku rake db:migrate
(in /app)
rake aborted!
uninitialized constant Rake::DSL
/usr/ruby1.9.2/lib/ruby/1.9.1/rake.rb:2482:in `const_missing'
/app/Rakefile:6:in `'
/usr/ruby1.9.2/lib/ruby/1.9.1/rake.rb:2373:in `load'
/usr/ruby1.9.2/lib/ruby/1.9.1/rake.rb:2373:in `raw_load_rakefile'
/usr/ruby1.9.2/lib/ruby/1.9.1/rake.rb:2007:in `block in load_rakefile'
/usr/ruby1.9.2/lib/ruby/1.9.1/rake.rb:2058:in `standard_exception_handling'
/usr/ruby1.9.2/lib/ruby/1.9.1/rake.rb:2006:in `load_rakefile'
/usr/ruby1.9.2/lib/ruby/1.9.1/rake.rb:1991:in `run'
/usr/ruby1.9.2/bin/rake:31:in `

'

Apparently, this is a well-documented error, and I've dug through a ton of Stack Overflow and Google discussion threads, trying various solutions but no luck so far.

I've manually set my rake gem to version 0.8.7, updated my GemFile and pushed changes to Git, which works for a lot of people, but not for me. Still, I'm not discouraged. I'll figure this out eventually. Just thought I'd throw this up here in case someone has had this exact error and found another solution.