diff --git a/lib/libc/Makefile b/lib/libc/Makefile
index 1015b053ebd8..f82a5b190a22 100644
--- a/lib/libc/Makefile
+++ b/lib/libc/Makefile
@@ -25,8 +25,10 @@ LIBC_ARCH=${MACHINE_CPUARCH}
 # excluded as a space-saving measure.  To produce a library that does
 # not contain these strings, add -DSTRIP_FBSDID (see <sys/cdefs.h>) to CFLAGS
 # below.  Note: there are no IDs for syscall stubs whose sources are generated.
-# To include legacy CSRG sccsid strings, add -DLIBC_SCCS and -DSYSLIBC_SCCS
-# to CFLAGS below.  -DSYSLIBC_SCCS affects just the system call stubs.
+# To include legacy CSRG SCCS ID strings, remove -DNO__SCCSID from CFLAGS.
+# To include RCS ID strings from other BSD projects, remove -DNO__RCSID from CFLAGS.
+CFLAGS+=-DNO__SCCSID -DNO__RCSID
+
 LIB=c
 SHLIB_MAJOR= 7
 .if ${MK_SSP} != "no"