diff --git a/lib/libc/include/libc_private.h b/lib/libc/include/libc_private.h
index f369cc7fe25c..d4265e9fcc1b 100644
--- a/lib/libc/include/libc_private.h
+++ b/lib/libc/include/libc_private.h
@@ -38,6 +38,8 @@
 #ifndef _LIBC_PRIVATE_H_
 #define _LIBC_PRIVATE_H_
 
+#include <spinlock.h>
+
 /*
  * This global flag is non-zero when a process has created one
  * or more threads. It is used to avoid calling locking functions
@@ -120,4 +122,10 @@ int _yp_check(char **);
  */
 extern const char *__progname;
 
+/*
+ * This is the lock to make malloc() thread-safe.  It is externalized
+ * so that thread libraries can protect malloc across fork().
+ */
+extern spinlock_t *__malloc_lock;
+
 #endif /* _LIBC_PRIVATE_H_ */
diff --git a/lib/libc/stdlib/malloc.c b/lib/libc/stdlib/malloc.c
index 7006df261e55..d99457abaa9a 100644
--- a/lib/libc/stdlib/malloc.c
+++ b/lib/libc/stdlib/malloc.c
@@ -74,6 +74,7 @@ __FBSDID("$FreeBSD$");
 #   include "libc_private.h"
 #   include "spinlock.h"
     static spinlock_t thread_lock	= _SPINLOCK_INITIALIZER;
+    spinlock_t *__malloc_lock		= &thread_lock;
 #   define _MALLOC_LOCK()		if (__isthreaded) _SPINLOCK(&thread_lock);
 #   define _MALLOC_UNLOCK()		if (__isthreaded) _SPINUNLOCK(&thread_lock);
 #endif /* __FreeBSD__ */