diff --git a/sys/src/kern/amd64/syscall.c b/sys/src/kern/amd64/syscall.c
index 33a2b9e..a44453a 100644
--- a/sys/src/kern/amd64/syscall.c
+++ b/sys/src/kern/amd64/syscall.c
@@ -238,6 +238,7 @@ syscall(Syscalls scallnr, Ureg* ureg)
 	m->syscall++;
 	up->inkernel = 1;
 	up->cursyscall = (Syscalls)scallnr;
+	up->blockingsc = 0;
 	up->pc = ureg->ip;
 	up->dbgreg = ureg;
 	if(up->trace && (pt = proctrace) != nil)
@@ -354,8 +355,13 @@ syscall(Syscalls scallnr, Ureg* ureg)
 	splhi();
 	if(scallnr != SysRfork && (up->procctl || up->nnote))
 		notify(ureg);
-	else if(canwakeup(scallnr))
-		awokeproc(up);
+	else if(up->blockingsc){
+		if(up->blockingsc != scallnr)
+			panic("syscall: up->blockingsc dirty");
+		if(canwakeup(scallnr))
+			awokeproc(up);
+		up->blockingsc = 0;
+	}
 
 	/* if we delayed sched because we held a lock, sched now */
 	if(up->delaysched){
diff --git a/sys/src/kern/port/awake.c b/sys/src/kern/port/awake.c
index 96e7bc7..7a09356 100644
--- a/sys/src/kern/port/awake.c
+++ b/sys/src/kern/port/awake.c
@@ -43,10 +43,9 @@ static Rendez	awaker;
 int
 canwakeup(Syscalls scall)
 {
-	if(scall == 0){
-		/* on page fault */
-		return 0;
-	}
+	if(scall == 0)
+		panic("canwakeup on page fault");
+
 	switch(scall){
 	default:
 		panic("canwakeup: unknown scall %d\n", scall);
diff --git a/sys/src/kern/port/portdat.h b/sys/src/kern/port/portdat.h
index dcd5316..729a24d 100644
--- a/sys/src/kern/port/portdat.h
+++ b/sys/src/kern/port/portdat.h
@@ -610,6 +610,9 @@ struct Proc
 
 	int		inkernel;	/* either on syscall or fault */
 	Syscalls	cursyscall;	/* zero on fault */
+	Syscalls	blockingsc;	/* set to cursyscall on sleep() and sysrendevouz
+					 * reset by syscall
+					 */
 
 	int32_t		blockingfd;	/* fd currenly read/written */
 
diff --git a/sys/src/kern/port/portfns.h b/sys/src/kern/port/portfns.h
index 6a421f0..a4312aa 100644
--- a/sys/src/kern/port/portfns.h
+++ b/sys/src/kern/port/portfns.h
@@ -33,7 +33,7 @@ int		anyhigher(void);
 int		anyready(void);
 void		awakekproc(void*);
 #define	awokeproc(p)	(p->lastWakeup = p->pendingWakeup)
-#define	awakeOnBlock(p)	(p->lastWakeup < p->pendingWakeup)
+#define	awakeOnBlock(p)	(p->blockingsc && p->lastWakeup < p->pendingWakeup)
 Block*		bl2mem(uint8_t*, Block*, int);
 int		blocklen(Block*);
 void		bootlinks(void);
diff --git a/sys/src/kern/port/proc.c b/sys/src/kern/port/proc.c
index b3e3b29..6ea1542 100644
--- a/sys/src/kern/port/proc.c
+++ b/sys/src/kern/port/proc.c
@@ -712,6 +712,7 @@ sleep(Rendez *r, int (*f)(void*), void *arg)
 	 */
 	r->p = up;
 
+	up->blockingsc = up->cursyscall;
 	if((*f)(arg)
 	|| (up->notepending && !up->notedeferred)
 	|| (up->inkernel && awakeOnBlock(up) && canwakeup(up->cursyscall))){
diff --git a/sys/src/kern/port/sysproc.c b/sys/src/kern/port/sysproc.c
index 94c2679..e742a9d 100644
--- a/sys/src/kern/port/sysproc.c
+++ b/sys/src/kern/port/sysproc.c
@@ -839,6 +839,7 @@ sysrendezvous(void* tagp, void* rendvalp)
 		l = &p->rendhash;
 	}
 
+	up->blockingsc = up->cursyscall;
 	if(awakeOnBlock(up)){
 		unlock(&up->rgrp->l);
 		result = UINT2PTR(up->rendval);