Pthread pid caching was removed recently but an assert is still present which checks pthread->pid, and this breaks the build when debugging is enabled: http://repo.or.cz/uclibc-ng.git/commit/bddde5860ffb8a78587854cc8e3e914bd692… http://repo.or.cz/uclibc-ng.git/blob/HEAD:/libpthread/nptl/pthread_getattr_… Line 69 should be removed from pthread_getattr_np.c . Cheers, Bogdan