diff --git a/lib/libc_r/Makefile b/lib/libc_r/Makefile
index 88f883cd272..63299eaad69 100644
--- a/lib/libc_r/Makefile
+++ b/lib/libc_r/Makefile
@@ -1,4 +1,4 @@
-#	$Id: Makefile,v 1.9 1998/05/31 23:53:50 jb Exp $
+#	$Id: Makefile,v 1.10 1998/06/01 02:12:15 jb Exp $
 #
 # All library objects contain rcsid strings by default; they may be
 # excluded as a space-saving measure.  To produce a library that does
@@ -10,6 +10,11 @@ SHLIB_MAJOR= 3
 SHLIB_MINOR= 0
 CFLAGS+=-DLIBC_RCS -DSYSLIBC_RCS -I${.CURDIR}/../libc/include
 CFLAGS+=-DPTHREAD_KERNEL -D_THREAD_SAFE -I${.CURDIR}/uthread
+
+# Uncomment this if you want libc_r to contain debug information for
+# thread locking.
+# CFLAGS+=-D_LOCK_DEBUG
+
 AINC=	-I${.CURDIR}/../libc/${MACHINE_ARCH} -I${.CURDIR}/uthread
 PRECIOUSLIB=	yes
 
diff --git a/lib/libkse/Makefile b/lib/libkse/Makefile
index 88f883cd272..63299eaad69 100644
--- a/lib/libkse/Makefile
+++ b/lib/libkse/Makefile
@@ -1,4 +1,4 @@
-#	$Id: Makefile,v 1.9 1998/05/31 23:53:50 jb Exp $
+#	$Id: Makefile,v 1.10 1998/06/01 02:12:15 jb Exp $
 #
 # All library objects contain rcsid strings by default; they may be
 # excluded as a space-saving measure.  To produce a library that does
@@ -10,6 +10,11 @@ SHLIB_MAJOR= 3
 SHLIB_MINOR= 0
 CFLAGS+=-DLIBC_RCS -DSYSLIBC_RCS -I${.CURDIR}/../libc/include
 CFLAGS+=-DPTHREAD_KERNEL -D_THREAD_SAFE -I${.CURDIR}/uthread
+
+# Uncomment this if you want libc_r to contain debug information for
+# thread locking.
+# CFLAGS+=-D_LOCK_DEBUG
+
 AINC=	-I${.CURDIR}/../libc/${MACHINE_ARCH} -I${.CURDIR}/uthread
 PRECIOUSLIB=	yes
 
diff --git a/lib/libpthread/Makefile b/lib/libpthread/Makefile
index 88f883cd272..63299eaad69 100644
--- a/lib/libpthread/Makefile
+++ b/lib/libpthread/Makefile
@@ -1,4 +1,4 @@
-#	$Id: Makefile,v 1.9 1998/05/31 23:53:50 jb Exp $
+#	$Id: Makefile,v 1.10 1998/06/01 02:12:15 jb Exp $
 #
 # All library objects contain rcsid strings by default; they may be
 # excluded as a space-saving measure.  To produce a library that does
@@ -10,6 +10,11 @@ SHLIB_MAJOR= 3
 SHLIB_MINOR= 0
 CFLAGS+=-DLIBC_RCS -DSYSLIBC_RCS -I${.CURDIR}/../libc/include
 CFLAGS+=-DPTHREAD_KERNEL -D_THREAD_SAFE -I${.CURDIR}/uthread
+
+# Uncomment this if you want libc_r to contain debug information for
+# thread locking.
+# CFLAGS+=-D_LOCK_DEBUG
+
 AINC=	-I${.CURDIR}/../libc/${MACHINE_ARCH} -I${.CURDIR}/uthread
 PRECIOUSLIB=	yes