Protobuf issues with imposm.parser on OS X El Capitan

Question

I have been trying to install imposm.parser on my MBPro (OSX El Capitan) via pip. I am getting the following error

In file included from imposm/parser/pbf/osm.cc:6:
    imposm/parser/pbf/osm.pb.h:9:10: fatal error: 'google/protobuf/stubs/common.h' file not found
    #include <google/protobuf/stubs/common.h>
         ^
    1 error generated.
    error: command '/usr/bin/clang' failed with exit status 1

I already installed protobuf and py2-protobuf using Macports. I also installed Google's Protocol Buffers 2.6.1 from source, but it does not address the issues. Note that the file common.h is actually in the google/protobuf/stubs folder when I checked.