diff --git a/src/class/cdc/cdc_device.c b/src/class/cdc/cdc_device.c
index 76526d40b..f8aa6824c 100644
--- a/src/class/cdc/cdc_device.c
+++ b/src/class/cdc/cdc_device.c
@@ -297,6 +297,7 @@ tusb_error_t cdcd_xfer_cb(uint8_t rhport, uint8_t ep_addr, tusb_event_t event, u
   uint8_t const itf = 0;
   cdcd_interface_t const * p_cdc = &_cdcd_itf[itf];
 
+  // receive new data
   if ( ep_addr == p_cdc->ep_out )
   {
     tu_fifo_write_n(&_rx_ff[itf], _tmp_rx_buf, xferred_bytes);
@@ -308,6 +309,8 @@ tusb_error_t cdcd_xfer_cb(uint8_t rhport, uint8_t ep_addr, tusb_event_t event, u
     if (tud_cdc_rx_cb) tud_cdc_rx_cb(itf);
   }
 
+  // nothing to do with in and notif endpoint
+
   return TUSB_ERROR_NONE;
 }
 
diff --git a/src/class/msc/msc_device.c b/src/class/msc/msc_device.c
index 71987addf..5ad8aa929 100644
--- a/src/class/msc/msc_device.c
+++ b/src/class/msc/msc_device.c
@@ -208,8 +208,6 @@ tusb_error_t mscd_xfer_cb(uint8_t rhport, uint8_t ep_addr, tusb_event_t event, u
   msc_cbw_t const * p_cbw = &p_msc->cbw;
   msc_csw_t       * p_csw = &p_msc->csw;
 
-  VERIFY( (ep_addr == p_msc->ep_out) || (ep_addr == p_msc->ep_in), TUSB_ERROR_INVALID_PARA);
-
   switch (p_msc->stage)
   {
     case MSC_STAGE_CMD:
diff --git a/src/device/usbd.c b/src/device/usbd.c
index d795e4f9a..e2ef5e7bb 100644
--- a/src/device/usbd.c
+++ b/src/device/usbd.c
@@ -269,14 +269,13 @@ static tusb_error_t usbd_main_st(void)
   }
   else if (USBD_EVT_XFER_DONE == event.event_id)
   {
-    // TODO only call respective interface callback
-    // Call class handling function. Those does not own the endpoint should check and return
-    for (uint8_t i = 0; i < USBD_CLASS_DRIVER_COUNT; i++)
+    // Invoke the class callback associated with the endpoint address
+    uint8_t const ep_addr = event.xfer_done.ep_addr;
+    uint8_t const drv_id  = _usbd_dev.ep2drv[ edpt_dir(ep_addr) ][ edpt_number(ep_addr) ];
+
+    if (drv_id < USBD_CLASS_DRIVER_COUNT)
     {
-      if ( usbd_class_drivers[i].xfer_cb )
-      {
-        usbd_class_drivers[i].xfer_cb( event.rhport, event.xfer_done.ep_addr, (tusb_event_t) event.xfer_done.result, event.xfer_done.xferred_byte);
-      }
+      usbd_class_drivers[drv_id].xfer_cb( event.rhport, ep_addr, (tusb_event_t) event.xfer_done.result, event.xfer_done.xferred_byte);
     }
   }
   else if (USBD_EVT_SOF == event.event_id)