--- Libc/Libc-262/threads/Makefile.inc
+++ Libc/Libc-583/threads/Makefile.inc
@@ -1,7 +1,5 @@
 .PATH: ${.CURDIR}/${MACHINE_ARCH}/threads ${.CURDIR}/threads
 
-.if exists(${.CURDIR}/${MACHINE_ARCH}/threads/Makefile.inc)
-.include "${.CURDIR}/${MACHINE_ARCH}/threads/Makefile.inc"
-.endif
+.sinclude "${.CURDIR}/${MACHINE_ARCH}/threads/Makefile.inc"
 
-SRCS += cprocs.c       cthreads.c     lu_utils.c     mig_support.c
+MISRCS += cprocs.c       cthreads.c     lu_utils.c     mig_support.c