diff --git a/lib/libc_r/Makefile b/lib/libc_r/Makefile
index 4c06007b566..ea000bda4a4 100644
--- a/lib/libc_r/Makefile
+++ b/lib/libc_r/Makefile
@@ -17,7 +17,7 @@ CFLAGS+=-I${.CURDIR}/../../include
 CFLAGS+=-D_LOCK_DEBUG
 
 # enable extra internal consistancy checks
-# CFLAGS+=-D_PTHREADS_INVARIANTS
+CFLAGS+=-D_PTHREADS_INVARIANTS
 
 AINC=	-I${.CURDIR}/../libc/${MACHINE_ARCH} -I${.CURDIR}/uthread
 PRECIOUSLIB=	yes
diff --git a/lib/libkse/Makefile b/lib/libkse/Makefile
index 4c06007b566..ea000bda4a4 100644
--- a/lib/libkse/Makefile
+++ b/lib/libkse/Makefile
@@ -17,7 +17,7 @@ CFLAGS+=-I${.CURDIR}/../../include
 CFLAGS+=-D_LOCK_DEBUG
 
 # enable extra internal consistancy checks
-# CFLAGS+=-D_PTHREADS_INVARIANTS
+CFLAGS+=-D_PTHREADS_INVARIANTS
 
 AINC=	-I${.CURDIR}/../libc/${MACHINE_ARCH} -I${.CURDIR}/uthread
 PRECIOUSLIB=	yes
diff --git a/lib/libpthread/Makefile b/lib/libpthread/Makefile
index 4c06007b566..ea000bda4a4 100644
--- a/lib/libpthread/Makefile
+++ b/lib/libpthread/Makefile
@@ -17,7 +17,7 @@ CFLAGS+=-I${.CURDIR}/../../include
 CFLAGS+=-D_LOCK_DEBUG
 
 # enable extra internal consistancy checks
-# CFLAGS+=-D_PTHREADS_INVARIANTS
+CFLAGS+=-D_PTHREADS_INVARIANTS
 
 AINC=	-I${.CURDIR}/../libc/${MACHINE_ARCH} -I${.CURDIR}/uthread
 PRECIOUSLIB=	yes