diff --git a/src/usb/setup.c b/src/usb/setup.c
index 8b800ea..624f301 100644
--- a/src/usb/setup.c
+++ b/src/usb/setup.c
@@ -138,8 +138,9 @@ static void write_configuration_descriptor(int wLength)
 {
 	usb_interface_t const * const *interfaces = usb_configure_interfaces();
 	size_t total_length = sizeof(usb_dc_configuration_t);
+    size_t interface_count = 0;
 
-	for(int i = 0; interfaces[i]; i++)
+	for(int i = 0; interfaces[i]; i++, interface_count++)
 	for(int k = 0; interfaces[i]->dc[k]; k++)
 	{
 		uint8_t const *dc = interfaces[i]->dc[k];
@@ -149,6 +150,7 @@ static void write_configuration_descriptor(int wLength)
 
 	/* Write the configuration descriptor */
 	dc_configuration.wTotalLength = htole16(total_length);
+    dc_configuration.bNumInterfaces = interface_count;
 	dcp_write(&dc_configuration, dc_configuration.bLength);
 	/* For the first call, the host usually wants only this */
 	if(wLength <= dc_configuration.bLength) return;