natpmp.h not picked up from contrib includes

Building using the contribs, I see this when running the daemon's configure script:

checking for natpmp.h... no
configure: WARNING: Unable to find the libnatpmp headers
          (you may need to install the dev package). You may use
          --without-natpmp to compile without NAT-PMP support.

Yet,

$ find -name natpmp.h
./contrib/native/natpmp/natpmp.h
./contrib/x86_64-unknown-linux-gnu/include/natpmp.h