readonly source broken?

with a readonly /usr/src  & /usr/obj (mounted via NFS from the machine
where "make buildworld" was run,
make installworld has the following error.
this seems wrong to me..


===> gnu/usr.bin/cvs/cvs (install)
install -s -o root -g wheel -m 555   cvs /usr/bin
install -o root -g wheel -m 444 cvs.1.gz  /usr/share/man/man1
install -o root -g wheel -m 444 cvs.5.gz  /usr/share/man/man5
===> gnu/usr.bin/cvs/contrib (install)
sed -e 's,_at_CSH_at_,/bin/csh,' -e 's,_at_PERL_at_,/usr/bin/perl,' /usr/src/gnu/usr.bin/cvs/contrib/../../../../contrib/cvs/contrib/Makefile.in > Makefile
cannot create Makefile: Read-only file system
*** Error code 2

Stop in /usr/src/gnu/usr.bin/cvs/contrib.
*** Error code 1

Stop in /usr/src/gnu/usr.bin/cvs.
*** Error code 1

Stop in /usr/src/gnu/usr.bin.
*** Error code 1