diff --git a/include/usb/usb_device.h b/include/usb/usb_device.h
index c383cafe48c..d8a76bd645e 100644
--- a/include/usb/usb_device.h
+++ b/include/usb/usb_device.h
@@ -157,6 +157,10 @@ struct usb_interface_cfg_data {
 	 * The custom request handler gets a first chance at handling
 	 * the request before it is handed over to the 'chapter 9' request
 	 * handler.
+	 * return 0 on success, -EINVAL if the request has not been handled by
+	 *	  the custom handler and instead needs to be handled by the
+	 *	  core USB stack. Any other error code to denote failure within
+	 *	  the custom handler.
 	 */
 	usb_request_handler custom_handler;
 };
diff --git a/samples/subsys/usb/webusb/src/main.c b/samples/subsys/usb/webusb/src/main.c
index df5749c4907..ca1135395be 100644
--- a/samples/subsys/usb/webusb/src/main.c
+++ b/samples/subsys/usb/webusb/src/main.c
@@ -212,7 +212,7 @@ int custom_handle_req(struct usb_setup_packet *pSetup,
 		return 0;
 	}
 
-	return -ENOTSUP;
+	return -EINVAL;
 }
 
 /**
diff --git a/samples/subsys/usb/webusb/src/webusb.c b/samples/subsys/usb/webusb/src/webusb.c
index 397ccca1ae3..69e17cf68c2 100644
--- a/samples/subsys/usb/webusb/src/webusb.c
+++ b/samples/subsys/usb/webusb/src/webusb.c
@@ -89,12 +89,11 @@ int webusb_custom_handle_req(struct usb_setup_packet *pSetup,
 	LOG_DBG("");
 
 	/* Call the callback */
-	if ((req_handlers && req_handlers->custom_handler) &&
-		(!req_handlers->custom_handler(pSetup, len, data))) {
-		return 0;
+	if (req_handlers && req_handlers->custom_handler) {
+		return req_handlers->custom_handler(pSetup, len, data);
 	}
 
-	return -ENOTSUP;
+	return -EINVAL;
 }
 
 /**
@@ -110,12 +109,11 @@ int webusb_vendor_handle_req(struct usb_setup_packet *pSetup,
 			     s32_t *len, u8_t **data)
 {
 	/* Call the callback */
-	if ((req_handlers && req_handlers->vendor_handler) &&
-		(!req_handlers->vendor_handler(pSetup, len, data))) {
-		return 0;
+	if (req_handlers && req_handlers->vendor_handler) {
+		return req_handlers->vendor_handler(pSetup, len, data);
 	}
 
-	return -ENOTSUP;
+	return -EINVAL;
 }
 
 /**
diff --git a/subsys/usb/class/hid/core.c b/subsys/usb/class/hid/core.c
index 47eac0abeca..08771997813 100644
--- a/subsys/usb/class/hid/core.c
+++ b/subsys/usb/class/hid/core.c
@@ -509,7 +509,7 @@ static int hid_custom_handle_req(struct usb_setup_packet *setup,
 		if (common == NULL) {
 			LOG_WRN("Device data not found for interface %u",
 				sys_le16_to_cpu(setup->wIndex));
-			return -ENODEV;
+			return -EINVAL;
 		}
 
 		dev_data = CONTAINER_OF(common, struct hid_device_info, common);
@@ -545,7 +545,7 @@ static int hid_custom_handle_req(struct usb_setup_packet *setup,
 		return 0;
 	}
 
-	return -ENOTSUP;
+	return -EINVAL;
 }
 
 static void hid_int_in(u8_t ep, enum usb_dc_ep_cb_status_code ep_status)
diff --git a/subsys/usb/class/usb_dfu.c b/subsys/usb/class/usb_dfu.c
index a6bbb05dcb9..80d42926e63 100644
--- a/subsys/usb/class/usb_dfu.c
+++ b/subsys/usb/class/usb_dfu.c
@@ -694,7 +694,7 @@ static int dfu_custom_handle_req(struct usb_setup_packet *pSetup,
 	}
 
 	/* Not handled by us */
-	return -ENOTSUP;
+	return -EINVAL;
 }
 
 static void dfu_interface_config(struct usb_desc_header *head,