diff --git a/usb/config.go b/usb/config.go
index b492e26..41142ac 100644
--- a/usb/config.go
+++ b/usb/config.go
@@ -44,14 +44,18 @@ type EndpointInfo struct {
 	UsageType UsageType
 }
 
-// String returns the human-readable description of the endpoint.
-func (e EndpointInfo) String() string {
+func (e EndpointInfo) addr() uint8 {
 	addr := e.Number
 	if e.Direction == EndpointDirectionIn {
 		addr |= 0x80
 	}
+	return addr
+}
+
+// String returns the human-readable description of the endpoint.
+func (e EndpointInfo) String() string {
 	ret := make([]string, 0, 3)
-	ret = append(ret, fmt.Sprintf("Endpoint #%d %s (address 0x%02x) %s", e.Number, e.Direction, addr, e.TransferType))
+	ret = append(ret, fmt.Sprintf("Endpoint #%d %s (address 0x%02x) %s", e.Number, e.Direction, e.addr(), e.TransferType))
 	switch e.TransferType {
 	case TransferTypeIsochronous:
 		ret = append(ret, fmt.Sprintf("- %s %s", e.IsoSyncType, e.UsageType))
diff --git a/usb/libusb.go b/usb/libusb.go
index e51f496..142f0b8 100644
--- a/usb/libusb.go
+++ b/usb/libusb.go
@@ -374,11 +374,7 @@ func (libusbImpl) alloc(d *libusbDevHandle, ep *EndpointInfo, timeout time.Durat
 		return nil, fmt.Errorf("libusb_alloc_transfer(%d) failed", isoPackets)
 	}
 	xfer.dev_handle = (*C.libusb_device_handle)(d)
-	addr := ep.Number & endpointNumMask
-	if ep.Direction == EndpointDirectionIn {
-		addr |= endpointDirectionMask
-	}
-	xfer.endpoint = C.uchar(addr)
+	xfer.endpoint = C.uchar(ep.addr())
 	xfer.timeout = C.uint(timeout / time.Millisecond)
 	xfer._type = C.uchar(ep.TransferType)
 	xfer.num_iso_packets = C.int(isoPackets)