diff --git a/sys/usb/usbus/cdc/acm/cdc_acm.c b/sys/usb/usbus/cdc/acm/cdc_acm.c
index 4d65762e8a64..4c9b347f1515 100644
--- a/sys/usb/usbus/cdc/acm/cdc_acm.c
+++ b/sys/usb/usbus/cdc/acm/cdc_acm.c
@@ -152,25 +152,14 @@ size_t usbus_cdc_acm_submit(usbus_cdcacm_device_t *cdcacm, const uint8_t *buf, s
 {
     size_t n;
     unsigned old;
-    if (cdcacm->state != USBUS_CDC_ACM_LINE_STATE_DISCONNECTED) {
-        old = irq_disable();
-        n = turb_add(&cdcacm->tsrb, buf, len);
-        irq_restore(old);
-        return n;
+    if (cdcacm->state == USBUS_CDC_ACM_LINE_STATE_DISCONNECTED) {
+        return len;
     }
-    /* stuff as much data as possible into tsrb, discarding the oldest */
+
     old = irq_disable();
-    n = turb_free(&cdcacm->tsrb);
-    if (len > n) {
-        n += turb_drop(&cdcacm->tsrb, len - n);
-        buf += len - n;
-    } else {
-        n = len;
-    }
-    turb_add(&cdcacm->tsrb, buf, n);
-    /* behave as if everything has been written correctly */
+    n = turb_add(&cdcacm->tsrb, buf, len);
     irq_restore(old);
-    return len;
+    return n;
 }
 
 void usbus_cdc_acm_set_coding_cb(usbus_cdcacm_device_t *cdcacm,
@@ -357,8 +346,12 @@ static void _transfer_handler(usbus_t *usbus, usbus_handler_t *handler,
 {
     (void)usbus;
     (void)event; /* Only receives TR_COMPLETE events */
+    if (ep->type != USB_EP_TYPE_BULK) {
+        return;
+    }
+
     usbus_cdcacm_device_t *cdcacm = (usbus_cdcacm_device_t*)handler;
-    if ((ep->dir == USB_EP_DIR_OUT) && (ep->type == USB_EP_TYPE_BULK)) {
+    if (ep->dir == USB_EP_DIR_OUT) {
         size_t len;
         /* Retrieve incoming data */
         usbdev_ep_get(ep, USBOPT_EP_AVAILABLE, &len, sizeof(size_t));
@@ -367,7 +360,7 @@ static void _transfer_handler(usbus_t *usbus, usbus_handler_t *handler,
         }
         usbdev_ep_xmit(ep, cdcacm->out_buf, CONFIG_USBUS_CDC_ACM_BULK_EP_SIZE);
     }
-    if ((ep->dir == USB_EP_DIR_IN) && (ep->type == USB_EP_TYPE_BULK)) {
+    else if (ep->dir == USB_EP_DIR_IN) {
         cdcacm->occupied = 0;
         if (!tsrb_empty(&cdcacm->tsrb)) {
             return _handle_in(cdcacm, ep);
diff --git a/sys/usb/usbus/cdc/acm/cdc_acm_stdio.c b/sys/usb/usbus/cdc/acm/cdc_acm_stdio.c
index fe171e74202b..64ab9bb1d700 100644
--- a/sys/usb/usbus/cdc/acm/cdc_acm_stdio.c
+++ b/sys/usb/usbus/cdc/acm/cdc_acm_stdio.c
@@ -51,9 +51,7 @@ static void _cdc_acm_rx_pipe(usbus_cdcacm_device_t *cdcacm,
                              uint8_t *data, size_t len)
 {
     (void)cdcacm;
-    for (size_t i = 0; i < len; i++) {
-        isrpipe_write_one(&stdin_isrpipe, data[i]);
-    }
+    isrpipe_write(&stdin_isrpipe, data, len);
 }
 
 void usb_cdc_acm_stdio_init(usbus_t *usbus)