Bad CPU Type in Executable

I have Mountain Lion. I'm trying to install the latest stable version Ruby from get.rvm.io, and I keep getting this error. How do I fix this?

[06:52 AM] ~ 4 $ curl -L https://get.rvm.io | bash -s stable --ruby

% Total % Received % Xferd Average Speed Time Time Time Current

Dload Upload Total Spent Left Speed

100 185 100 185 0 0 165 0 0:00:01 0:00:01 --:--:-- 319

100 9979 100 9979 0 0 5848 0 0:00:01 0:00:01 --:--:-- 45986

bash: line 30: /sw/bin/gtar: Bad CPU type in executable

Please read and follow further instructions.

Press ENTER to continue.

Downloading RVM from wayneeseguin branch stable

% Total % Received % Xferd Average Speed Time Time Time Current

Dload Upload Total Spent Left Speed

100 125 100 125 0 0 155 0 --:--:-- --:--:-- --:--:-- 287

100 1045k 100 1045k 0 0 525k 0 0:00:01 0:00:01 --:--:-- 2588k

bash: line 161: /sw/bin/gtar: Bad CPU type in executable

Could not extract RVM sources.

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