diff --git a/sys/kern/kern_lwp.c b/sys/kern/kern_lwp.c
index 2e072cc2a8bf..8dfe95e0c216 100644
--- a/sys/kern/kern_lwp.c
+++ b/sys/kern/kern_lwp.c
@@ -1,7 +1,7 @@
-/*	$NetBSD: kern_lwp.c,v 1.126 2008/10/28 22:11:36 wrstuden Exp $	*/
+/*	$NetBSD: kern_lwp.c,v 1.127 2009/02/04 21:17:39 ad Exp $	*/
 
 /*-
- * Copyright (c) 2001, 2006, 2007, 2008 The NetBSD Foundation, Inc.
+ * Copyright (c) 2001, 2006, 2007, 2008, 2009 The NetBSD Foundation, Inc.
  * All rights reserved.
  *
  * This code is derived from software contributed to The NetBSD Foundation
@@ -206,7 +206,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: kern_lwp.c,v 1.126 2008/10/28 22:11:36 wrstuden Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_lwp.c,v 1.127 2009/02/04 21:17:39 ad Exp $");
 
 #include "opt_ddb.h"
 #include "opt_lockdebug.h"
@@ -1388,6 +1388,47 @@ lwp_drainrefs(struct lwp *l)
 		cv_wait(&p->p_lwpcv, p->p_lock);
 }
 
+/*
+ * Return true if the specified LWP is 'alive'.  Only p->p_lock need
+ * be held.
+ */
+bool
+lwp_alive(lwp_t *l)
+{
+
+	KASSERT(mutex_owned(l->l_proc->p_lock));
+
+	switch (l->l_stat) {
+	case LSSLEEP:
+	case LSRUN:
+	case LSONPROC:
+	case LSSTOP:
+	case LSSUSPENDED:
+		return true;
+	default:
+		return false;
+	}
+}
+
+/*
+ * Return first live LWP in the process.
+ */
+lwp_t *
+lwp_find_first(proc_t *p)
+{
+	lwp_t *l;
+
+	KASSERT(mutex_owned(p->p_lock));
+
+	LIST_FOREACH(l, &p->p_lwps, l_sibling) {
+		if (lwp_alive(l)) {
+			return l;
+		}
+	}
+
+	return NULL;
+}
+
 /*
  * lwp_specific_key_create --
  *	Create a key for subsystem lwp-specific data.
diff --git a/sys/kern/sys_process.c b/sys/kern/sys_process.c
index dd7b9bfd92dc..49039cbc353d 100644
--- a/sys/kern/sys_process.c
+++ b/sys/kern/sys_process.c
@@ -1,9 +1,12 @@
-/*	$NetBSD: sys_process.c,v 1.145 2009/01/22 14:38:35 yamt Exp $	*/
+/*	$NetBSD: sys_process.c,v 1.146 2009/02/04 21:17:39 ad Exp $	*/
 
 /*-
- * Copyright (c) 2008 The NetBSD Foundation, Inc.
+ * Copyright (c) 2008, 2009 The NetBSD Foundation, Inc.
  * All rights reserved.
  *
+ * This code is derived from software contributed to The NetBSD Foundation
+ * by Andrew Doran.
+ *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
@@ -115,7 +118,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: sys_process.c,v 1.145 2009/01/22 14:38:35 yamt Exp $");
+__KERNEL_RCSID(0, "$NetBSD: sys_process.c,v 1.146 2009/02/04 21:17:39 ad Exp $");
 
 #include "opt_ptrace.h"
 #include "opt_ktrace.h"
@@ -337,10 +340,16 @@ sys_ptrace(struct lwp *l, const struct sys_ptrace_args *uap, register_t *retval)
 		break;
 	}
 
-	if (error == 0)
+	if (error == 0) {
 		error = kauth_authorize_process(l->l_cred,
 		    KAUTH_PROCESS_PTRACE, t, KAUTH_ARG(req),
 		    NULL, NULL);
+	}
+	if (error == 0) {
+		lt = lwp_find_first(t);
+		if (lt == NULL)
+			error = ESRCH;
+	}
 
 	if (error != 0) {
 		mutex_exit(proc_lock);
@@ -351,16 +360,6 @@ sys_ptrace(struct lwp *l, const struct sys_ptrace_args *uap, register_t *retval)
 
 	/* Do single-step fixup if needed. */
 	FIX_SSTEP(t);
-
-	/*
-	 * XXX NJWLWP
-	 *
-	 * The entire ptrace interface needs work to be useful to a
-	 * process with multiple LWPs. For the moment, we'll kluge
-	 * this; memory access will be fine, but register access will
-	 * be weird.
-	 */
-	lt = LIST_FIRST(&t->p_lwps);
 	KASSERT(lt != NULL);
 	lwp_addref(lt);
 
@@ -641,7 +640,7 @@ sys_ptrace(struct lwp *l, const struct sys_ptrace_args *uap, register_t *retval)
 		lwp_delref(lt);
 		mutex_enter(t->p_lock);
 		if (tmp == 0)
-			lt = LIST_FIRST(&t->p_lwps);
+			lt = lwp_find_first(t);
 		else {
 			lt = lwp_find(t, tmp);
 			if (lt == NULL) {
@@ -651,7 +650,7 @@ sys_ptrace(struct lwp *l, const struct sys_ptrace_args *uap, register_t *retval)
 			}
 			lt = LIST_NEXT(lt, l_sibling);
 		}
-		while (lt != NULL && lt->l_stat == LSZOMB)
+		while (lt != NULL && !lwp_alive(lt))
 			lt = LIST_NEXT(lt, l_sibling);
 		pl.pl_lwpid = 0;
 		pl.pl_event = 0;
diff --git a/sys/sys/lwp.h b/sys/sys/lwp.h
index de4b77737ef0..1e8cfbd69171 100644
--- a/sys/sys/lwp.h
+++ b/sys/sys/lwp.h
@@ -1,7 +1,7 @@
-/*	$NetBSD: lwp.h,v 1.116 2009/01/11 02:45:55 christos Exp $	*/
+/*	$NetBSD: lwp.h,v 1.117 2009/02/04 21:17:39 ad Exp $	*/
 
 /*-
- * Copyright (c) 2001, 2006, 2007, 2008 The NetBSD Foundation, Inc.
+ * Copyright (c) 2001, 2006, 2007, 2008, 2009 The NetBSD Foundation, Inc.
  * All rights reserved.
  *
  * This code is derived from software contributed to The NetBSD Foundation
@@ -282,6 +282,8 @@ int	lwp_trylock(lwp_t *);
 void	lwp_addref(lwp_t *);
 void	lwp_delref(lwp_t *);
 void	lwp_drainrefs(lwp_t *);
+bool	lwp_alive(lwp_t *);
+lwp_t	*lwp_find_first(proc_t *);
 
 /* Flags for _lwp_wait1 */
 #define LWPWAIT_EXITCONTROL	0x00000001