[CentOS] Can't build RPM for i686 target (i386 works)

I'm creating a simple RPM for my 32-bit CentOS 6 server.  When I build
the RPM without specifying a target architecture (rpmbuild foo.spec), it
successfully builds an i386 RPM.

If I try to build an i686 RPM, I get nothing:

  $ rpmbuild --target i686 foo.spec
  Building target platforms: i686
  Building for target i686

And I'm returned to command prompt with no error message.  The SPEC file
doesn't contain any architecture-related tags.

I feel like I must be missing something really, really basic, but I'll
be darned if I can figure out what it might be.

Any ideas?

-- 
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Ian Pilcher                                         arequipeno at gmail.com
-------- "I grew up before Mark Zuckerberg invented friendship" --------
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