diff --git a/src/class/dfu/dfu_rt_device.c b/src/class/dfu/dfu_rt_device.c
index 0ef5fe63f..426680e8e 100644
--- a/src/class/dfu/dfu_rt_device.c
+++ b/src/class/dfu/dfu_rt_device.c
@@ -56,24 +56,25 @@ void dfu_rtd_reset(uint8_t rhport)
   (void) rhport;
 }
 
-bool dfu_rtd_open(uint8_t rhport, tusb_desc_interface_t const * itf_desc, uint16_t *p_length)
+uint16_t dfu_rtd_open(uint8_t rhport, tusb_desc_interface_t const * itf_desc, uint16_t max_len)
 {
   (void) rhport;
+  (void) max_len;
 
   // Ensure this is DFU Runtime
-  TU_VERIFY(itf_desc->bInterfaceSubClass == TUD_DFU_APP_SUBCLASS);
-  TU_VERIFY(itf_desc->bInterfaceProtocol == DFU_PROTOCOL_RT);
+  TU_VERIFY(itf_desc->bInterfaceSubClass == TUD_DFU_APP_SUBCLASS &&
+            itf_desc->bInterfaceProtocol == DFU_PROTOCOL_RT, 0);
 
   uint8_t const * p_desc = tu_desc_next( itf_desc );
-  (*p_length) = sizeof(tusb_desc_interface_t);
+  uint16_t len = sizeof(tusb_desc_interface_t);
 
   if ( TUSB_DESC_FUNCTIONAL == tu_desc_type(p_desc) )
   {
-    (*p_length) += p_desc[DESC_OFFSET_LEN];
+    len += tu_desc_len(p_desc);
     p_desc = tu_desc_next(p_desc);
   }
 
-  return true;
+  return len;
 }
 
 bool dfu_rtd_control_complete(uint8_t rhport, tusb_control_request_t const * request)
diff --git a/src/class/dfu/dfu_rt_device.h b/src/class/dfu/dfu_rt_device.h
index 294d993e3..91ead88c6 100644
--- a/src/class/dfu/dfu_rt_device.h
+++ b/src/class/dfu/dfu_rt_device.h
@@ -63,12 +63,12 @@ TU_ATTR_WEAK void tud_dfu_rt_reboot_to_dfu(void); // TODO rename to _cb conventi
 //--------------------------------------------------------------------+
 // Internal Class Driver API
 //--------------------------------------------------------------------+
-void dfu_rtd_init(void);
-void dfu_rtd_reset(uint8_t rhport);
-bool dfu_rtd_open(uint8_t rhport, tusb_desc_interface_t const * itf_desc, uint16_t *p_length);
-bool dfu_rtd_control_request(uint8_t rhport, tusb_control_request_t const * request);
-bool dfu_rtd_control_complete(uint8_t rhport, tusb_control_request_t const * request);
-bool dfu_rtd_xfer_cb(uint8_t rhport, uint8_t ep_addr, xfer_result_t event, uint32_t xferred_bytes);
+void     dfu_rtd_init(void);
+void     dfu_rtd_reset(uint8_t rhport);
+uint16_t dfu_rtd_open(uint8_t rhport, tusb_desc_interface_t const * itf_desc, uint16_t max_len);
+bool     dfu_rtd_control_request(uint8_t rhport, tusb_control_request_t const * request);
+bool     dfu_rtd_control_complete(uint8_t rhport, tusb_control_request_t const * request);
+bool     dfu_rtd_xfer_cb(uint8_t rhport, uint8_t ep_addr, xfer_result_t event, uint32_t xferred_bytes);
 
 #ifdef __cplusplus
  }