--- Libc/Libc-498.1.5/threads/Makefile.inc
+++ Libc/Libc-391/threads/Makefile.inc
@@ -1,5 +1,7 @@
 .PATH: ${.CURDIR}/${MACHINE_ARCH}/threads ${.CURDIR}/threads
 
-.sinclude "${.CURDIR}/${MACHINE_ARCH}/threads/Makefile.inc"
+.if exists(${.CURDIR}/${MACHINE_ARCH}/threads/Makefile.inc)
+.include "${.CURDIR}/${MACHINE_ARCH}/threads/Makefile.inc"
+.endif
 
 MISRCS += cprocs.c       cthreads.c     lu_utils.c     mig_support.c