diff --git a/sys/src/9/port/proc.c b/sys/src/9/port/proc.c
index e1acf340e..c8deaa401 100644
--- a/sys/src/9/port/proc.c
+++ b/sys/src/9/port/proc.c
@@ -1820,6 +1820,19 @@ procindex(ulong pid)
 	return -1;
 }
 
+/*
+ *  for the following functions:
+ *    setnoteid(), pidalloc() and pidfree()
+ *
+ *  They need to be called with p->debug held
+ *  to prevent devproc's changenoteid() from
+ *  changing the noteid under us and make the
+ *  update atomic.
+ */
+
+/*
+ *  change the noteid of a process
+ */
 ulong
 setnoteid(Proc *p, ulong noteid)
 {
@@ -1840,15 +1853,6 @@ setnoteid(Proc *p, ulong noteid)
 	return p->noteid = i->pid;
 }
 
-static ulong
-setparentpid(Proc *p, Proc *pp)
-{
-	Pid *i;
-
-	i = pidadd(pp->pid);
-	return p->parentpid = i->pid;
-}
-
 /*
  *  allocate pid, noteid and parentpid to a process
  */
@@ -1858,8 +1862,11 @@ pidalloc(Proc *p)
 	Pid *i;
 
 	/* skip for the boot process */
-	if(up != nil)
-		setparentpid(p, up);
+	if(up != nil){
+		i = pidadd(up->pid);
+		p->parentpid = i->pid;
+	} else
+		p->parentpid = 0;
 
 	i = pidadd(0);
 	i->procindex = (int)(p - procalloc.arena);
diff --git a/sys/src/9/port/sysproc.c b/sys/src/9/port/sysproc.c
index f451e047d..b3b7a0439 100644
--- a/sys/src/9/port/sysproc.c
+++ b/sys/src/9/port/sysproc.c
@@ -79,14 +79,18 @@ sysrfork(va_list list)
 				envcpy(up->egrp, oeg);
 			closeegrp(oeg);
 		}
-		if(flag & RFNOTEG)
-			setnoteid(up, 0);
+		if(flag & RFNOTEG){
+			qlock(&up->debug);
+			setnoteid(up, 0);	/* can't error() with 0 argument */
+			qunlock(&up->debug);
+		}
 		return 0;
 	}
 
 	if((p = newproc()) == nil)
 		error("no procs");
 
+	qlock(&up->debug);
 	qlock(&p->debug);
 
 	p->scallnr = up->scallnr;
@@ -112,7 +116,8 @@ sysrfork(va_list list)
 		p->procctl = Proc_tracesyscall;
 	p->kp = 0;
 
-	/* Craft a return frame which will cause the child to pop out of
+	/*
+	 * Craft a return frame which will cause the child to pop out of
 	 * the scheduler in user mode with the return register zero
 	 */
 	forkchild(p, up->dbgreg);
@@ -132,6 +137,7 @@ sysrfork(va_list list)
 	pid = pidalloc(p);
 
 	qunlock(&p->debug);
+	qunlock(&up->debug);
 
 	/* Abort the child process on error */
 	if(waserror()){