diff --git a/lib/usb.c b/lib/usb.c
index 625c74f..c8e4790 100644
--- a/lib/usb.c
+++ b/lib/usb.c
@@ -38,10 +38,10 @@ usb_dev_handle *open_usb(uint16_t default_vendor, uint16_t default_product)
 	for (bus = usb_get_busses(); bus; bus = bus->next)
 		for (dev = bus->devices; dev; dev = dev->next) {
 			if (dev->descriptor.idVendor !=
-			    vendor ? vendor : default_vendor)
+			    (vendor ? vendor : default_vendor))
 				continue;
 			if (dev->descriptor.idProduct !=
-			    product ? product : default_product)
+			    (product ? product : default_product))
 				continue;
 			handle = usb_open(dev);
 #ifdef DO_FULL_USB_BUREAUCRACY