diff --git a/demos/various/SB-CLIENT-32k-08070000-16k-20018000/main.c b/demos/various/SB-CLIENT-32k-08070000-16k-20018000/main.c
index 094c8f62f..889641d66 100644
--- a/demos/various/SB-CLIENT-32k-08070000-16k-20018000/main.c
+++ b/demos/various/SB-CLIENT-32k-08070000-16k-20018000/main.c
@@ -46,6 +46,11 @@ int main(void) {
   halInit();
   chSysInit();
 
+  /*
+   * Activates the Serial or SIO driver using the default configuration.
+   */
+  sioStart(&SIOD1, NULL);
+
   /* Creating a blinker thread.*/
   chThdCreateStatic(waThread1, sizeof(waThread1), NORMALPRIO+10, Thread1, NULL);
 
diff --git a/os/sb/vio/sbvio_uart.c b/os/sb/vio/sbvio_uart.c
index 25f9a9a1e..66167f6cf 100644
--- a/os/sb/vio/sbvio_uart.c
+++ b/os/sb/vio/sbvio_uart.c
@@ -60,10 +60,10 @@ static void vuart_cb(SIODriver *siop) {
 
 void sb_api_vio_uart(struct port_extctx *ectxp) {
   sb_class_t *sbp = (sb_class_t *)chThdGetSelfX()->ctx.syscall.p;
+  uint32_t sub  = ectxp->r0;
+  uint32_t unit = ectxp->r1;
   ectxp->r0 = (uint32_t)CH_RET_INNER_ERROR;
   ectxp->r1 = (uint32_t)0;
-  uint32_t sub = ectxp->r0;
-  uint32_t unit = ectxp->r1;
   const vio_uart_unit_t *unitp;
 
   if (unit >= sbp->config->vioconf->uarts->n) {