diff --git a/unix/mkfile.mk b/unix/mkfile.mk
index 6d650fe..09d064d 100644
--- a/unix/mkfile.mk
+++ b/unix/mkfile.mk
@@ -6,6 +6,7 @@
 	Makefile\
 	mk.1\
 	mk.h\
+	sys.h\
 	fns.h\
 	`{ls -p $PLAN9/src/cmd/mk/*.c}\
 
@@ -37,3 +38,6 @@
 
 NOTICE: ../NOTICE.mk
 	cp $prereq $target
+
+sys.h: $PLAN9/src/cmd/mk/sys.h.std
+	cp $prereq $target