Build from source for MacOS Sierra - gfortran error

[dugtil]

I'm attempting to build opensees from source on MacOS Sierra 10.12.6.

First lines after "make":

Making idamax.o from idamax.f
/usr/local/bin/gfortran -Wall -O -DCUBLAS -x f77-cpp-input --no-second-underscore -c idamax.f -o idamax.o
FATAL:/opt/local/bin/../libexec/as/x86_64/as: I don't understand 'm' flag!
make[1]: *** [idamax.o] Error 1

I'm using gcc version 6.3.0. The Makefile.def comes from "Makefile.def.MacOS10.8" with minor changes.

Anyone coming across this error?