diff --git a/sys/src/9/kw/syscall.c b/sys/src/9/kw/syscall.c
index 555d767ee..30cc29c40 100644
--- a/sys/src/9/kw/syscall.c
+++ b/sys/src/9/kw/syscall.c
@@ -78,6 +78,7 @@ noted(Ureg* cur, uintptr arg0)
 		nf->arg0 = &nf->ureg;
 		nf->ip = 0;
 		cur->sp = PTR2UINT(nf);
+		cur->r0 = PTR2UINT(nf->arg0);
 		break;
 	default:
 		up->lastnote.flag = NDebug;
@@ -163,6 +164,8 @@ notify(Ureg* ureg)
 
 	ureg->sp = sp;
 	ureg->pc = PTR2UINT(up->notify);
+	ureg->r0 = PTR2UINT(nf->arg0);
+
 	up->notified = 1;
 	up->nnote--;
 	memmove(&up->lastnote, &up->note[0], sizeof(Note));
diff --git a/sys/src/9/omap/syscall.c b/sys/src/9/omap/syscall.c
index 224ee2c29..882aef2cc 100644
--- a/sys/src/9/omap/syscall.c
+++ b/sys/src/9/omap/syscall.c
@@ -78,6 +78,7 @@ noted(Ureg* cur, uintptr arg0)
 		nf->arg0 = &nf->ureg;
 		nf->ip = 0;
 		cur->sp = PTR2UINT(nf);
+		cur->r0 = PTR2UINT(nf->arg0);
 		break;
 	default:
 		up->lastnote.flag = NDebug;
@@ -163,6 +164,8 @@ notify(Ureg* ureg)
 
 	ureg->sp = sp;
 	ureg->pc = PTR2UINT(up->notify);
+	ureg->r0 = PTR2UINT(nf->arg0);
+
 	up->notified = 1;
 	up->nnote--;
 	memmove(&up->lastnote, &up->note[0], sizeof(Note));
diff --git a/sys/src/9/teg2/syscall.c b/sys/src/9/teg2/syscall.c
index 4bdfc4edb..be24849b2 100644
--- a/sys/src/9/teg2/syscall.c
+++ b/sys/src/9/teg2/syscall.c
@@ -84,6 +84,7 @@ noted(Ureg* cur, uintptr arg0)
 		nf->arg0 = &nf->ureg;
 		nf->ip = 0;
 		cur->sp = PTR2UINT(nf);
+		cur->r0 = PTR2UINT(nf->arg0);
 		break;
 	default:
 		up->lastnote.flag = NDebug;
@@ -169,6 +170,7 @@ notify(Ureg* ureg)
 
 	ureg->sp = sp;
 	ureg->pc = PTR2UINT(up->notify);
+	ureg->r0 = PTR2UINT(nf->arg0);
 
 	up->notified = 1;
 	up->nnote--;
diff --git a/sys/src/9/zynq/trap.c b/sys/src/9/zynq/trap.c
index 54e445899..510860b63 100644
--- a/sys/src/9/zynq/trap.c
+++ b/sys/src/9/zynq/trap.c
@@ -423,6 +423,7 @@ noted(Ureg *ureg, ulong arg0)
 		sp = oureg - 4 * BY2WD - ERRMAX;
 		splhi();
 		ureg->sp = sp;
+		ureg->r0 = (uintptr) oureg;
 		((ulong *) sp)[1] = oureg;
 		((ulong *) sp)[0] = 0;
 		break;