Refreshing an individual gemspec

I’m in the process of upgrading a rails app from 2.1 to 2.3, and 2.3 wants me to refresh some of the gemspecs for my vendored gems. Unfortunately, when I run rake gems:refresh_specs I get the dreaded:

rake aborted!
can't activate , already activated json-1.1.9

I was able to refresh the spec in question outside of rake with (in the console):

>> Rails::GemDependency.from_directory_name('vendor/gems/gem_name-0.1.0', false).refresh

Hopefully that helps someone else out.