diff --git a/src/class/hid/hid_device.c b/src/class/hid/hid_device.c
index cbdc5bece..51bd153ec 100644
--- a/src/class/hid/hid_device.c
+++ b/src/class/hid/hid_device.c
@@ -158,11 +158,12 @@ void hidd_reset(uint8_t rhport)
   tu_memclr(_hidd_itf, sizeof(_hidd_itf));
 }
 
-bool hidd_open(uint8_t rhport, tusb_desc_interface_t const * desc_itf, uint16_t *p_len)
+uint16_t hidd_open(uint8_t rhport, tusb_desc_interface_t const * desc_itf, uint16_t max_len)
 {
-  TU_VERIFY(TUSB_CLASS_HID == desc_itf->bInterfaceClass);
+  TU_VERIFY(TUSB_CLASS_HID == desc_itf->bInterfaceClass, 0);
 
-  uint8_t const *p_desc = (uint8_t const *) desc_itf;
+  // max length is at least interface + hid descriptor + 1 endpoint
+  TU_ASSERT(max_len >= sizeof(tusb_desc_interface_t) + sizeof(tusb_hid_descriptor_hid_t) + sizeof(tusb_desc_endpoint_t), 0);
 
   // Find available interface
   hidd_interface_t * p_hid = NULL;
@@ -175,16 +176,18 @@ bool hidd_open(uint8_t rhport, tusb_desc_interface_t const * desc_itf, uint16_t
       break;
     }
   }
-  TU_ASSERT(p_hid);
+  TU_ASSERT(p_hid, 0);
+
+  uint8_t const *p_desc = (uint8_t const *) desc_itf;
 
   //------------- HID descriptor -------------//
   p_desc = tu_desc_next(p_desc);
   p_hid->hid_descriptor = (tusb_hid_descriptor_hid_t const *) p_desc;
-  TU_ASSERT(HID_DESC_TYPE_HID == p_hid->hid_descriptor->bDescriptorType);
+  TU_ASSERT(HID_DESC_TYPE_HID == p_hid->hid_descriptor->bDescriptorType, 0);
 
   //------------- Endpoint Descriptor -------------//
   p_desc = tu_desc_next(p_desc);
-  TU_ASSERT(usbd_open_edpt_pair(rhport, p_desc, desc_itf->bNumEndpoints, TUSB_XFER_INTERRUPT, &p_hid->ep_out, &p_hid->ep_in));
+  TU_ASSERT(usbd_open_edpt_pair(rhport, p_desc, desc_itf->bNumEndpoints, TUSB_XFER_INTERRUPT, &p_hid->ep_out, &p_hid->ep_in), 0);
 
   if ( desc_itf->bInterfaceSubClass == HID_SUBCLASS_BOOT ) p_hid->boot_protocol = desc_itf->bInterfaceProtocol;
 
@@ -192,12 +195,10 @@ bool hidd_open(uint8_t rhport, tusb_desc_interface_t const * desc_itf, uint16_t
   p_hid->itf_num   = desc_itf->bInterfaceNumber;
   memcpy(&p_hid->report_desc_len, &(p_hid->hid_descriptor->wReportLength), 2);
 
-  *p_len = sizeof(tusb_desc_interface_t) + sizeof(tusb_hid_descriptor_hid_t) + desc_itf->bNumEndpoints*sizeof(tusb_desc_endpoint_t);
-
   // Prepare for output endpoint
-  if (p_hid->ep_out) TU_ASSERT(usbd_edpt_xfer(rhport, p_hid->ep_out, p_hid->epout_buf, sizeof(p_hid->epout_buf)));
+  if (p_hid->ep_out) TU_ASSERT(usbd_edpt_xfer(rhport, p_hid->ep_out, p_hid->epout_buf, sizeof(p_hid->epout_buf)), 0);
 
-  return true;
+  return sizeof(tusb_desc_interface_t) + sizeof(tusb_hid_descriptor_hid_t) + desc_itf->bNumEndpoints*sizeof(tusb_desc_endpoint_t);
 }
 
 // Handle class control request
diff --git a/src/class/hid/hid_device.h b/src/class/hid/hid_device.h
index efdde9569..ad8c9ece4 100644
--- a/src/class/hid/hid_device.h
+++ b/src/class/hid/hid_device.h
@@ -300,12 +300,12 @@ TU_ATTR_WEAK bool tud_hid_set_idle_cb(uint8_t idle_rate);
 //--------------------------------------------------------------------+
 // Internal Class Driver API
 //--------------------------------------------------------------------+
-void hidd_init             (void);
-void hidd_reset            (uint8_t rhport);
-bool hidd_open             (uint8_t rhport, tusb_desc_interface_t const * itf_desc, uint16_t *p_length);
-bool hidd_control_request  (uint8_t rhport, tusb_control_request_t const * request);
-bool hidd_control_complete (uint8_t rhport, tusb_control_request_t const * request);
-bool hidd_xfer_cb          (uint8_t rhport, uint8_t ep_addr, xfer_result_t event, uint32_t xferred_bytes);
+void     hidd_init             (void);
+void     hidd_reset            (uint8_t rhport);
+uint16_t hidd_open             (uint8_t rhport, tusb_desc_interface_t const * itf_desc, uint16_t max_len);
+bool     hidd_control_request  (uint8_t rhport, tusb_control_request_t const * request);
+bool     hidd_control_complete (uint8_t rhport, tusb_control_request_t const * request);
+bool     hidd_xfer_cb          (uint8_t rhport, uint8_t ep_addr, xfer_result_t event, uint32_t xferred_bytes);
 
 #ifdef __cplusplus
  }
diff --git a/src/class/msc/msc_device.c b/src/class/msc/msc_device.c
index 0ae25f89a..c3ce495e1 100644
--- a/src/class/msc/msc_device.c
+++ b/src/class/msc/msc_device.c
@@ -165,7 +165,7 @@ uint16_t mscd_open(uint8_t rhport, tusb_desc_interface_t const * itf_desc, uint1
   enum { _MSC_DRIVER_LEN = sizeof(tusb_desc_interface_t) + 2*sizeof(tusb_desc_endpoint_t) };
 
   // Max length mus be at least 1 interface + 2 endpoints
-  TU_VERIFY(max_len >= _MSC_DRIVER_LEN, 0);
+  TU_ASSERT(max_len >= _MSC_DRIVER_LEN, 0);
 
   mscd_interface_t * p_msc = &_mscd_itf;
   p_msc->itf_num = itf_desc->bInterfaceNumber;