diff --git a/include/libopencm3/usb/usbd.h b/include/libopencm3/usb/usbd.h
index 9da83796..8f685557 100644
--- a/include/libopencm3/usb/usbd.h
+++ b/include/libopencm3/usb/usbd.h
@@ -24,6 +24,13 @@
 
 BEGIN_DECLS
 
+
+enum usbd_request_return_codes {
+	USBD_REQ_NOTSUPP	= 0,
+	USBD_REQ_HANDLED	= 1,
+	USBD_REQ_NEXT_CALLBACK	= 2,
+};
+
 typedef struct _usbd_driver usbd_driver;
 extern const usbd_driver stm32f103_usb_driver;
 extern const usbd_driver stm32f107_usb_driver;
diff --git a/lib/usb/usb_control.c b/lib/usb/usb_control.c
index 3dd08578..b4ac57e9 100644
--- a/lib/usb/usb_control.c
+++ b/lib/usb/usb_control.c
@@ -102,7 +102,8 @@ static int usb_control_request_dispatch(struct usb_setup_data *req)
 			result = cb[i].cb(req, &control_state.ctrl_buf,
 					  &control_state.ctrl_len,
 					  &control_state.complete);
-			if (result)
+			if (result == USBD_REQ_HANDLED ||
+			    result == USBD_REQ_NOTSUPP)
 				return result;
 		}
 	}