diff --git a/src/types/usb_device.rs b/src/types/usb_device.rs
index 8db5d29..9881ef6 100644
--- a/src/types/usb_device.rs
+++ b/src/types/usb_device.rs
@@ -84,6 +84,8 @@ pub(crate) const ONE_MS_16_MGHZ: u32 = 16000;
 const UDINT_BYTE: u8 = 0x7d;
 const USBINT_BYTE: u8 = 0x01;
 const UEINTX_BYTE: u8 = 0xdf;
+const UENUM_MASK: u8 = 0b111;
+
 pub(crate) trait InterruptCleaner {
     fn clear_interrupts(&mut self) -> &mut Self;
 }
@@ -142,9 +144,8 @@ impl<const L: usize> UsbDevice<L> {
         endpoint_index: usize,
     ) -> Result<(), UsbError> {
         let usb = self.usb.borrow(cs);
-        let endpoint_index = endpoint_index as u8;
 
-        if endpoint_index >= 7 {
+        if endpoint_index >= MAX_ENDPOINTS {
             return Err(UsbError::InvalidEndpoint);
         }
 
@@ -152,9 +153,9 @@ impl<const L: usize> UsbDevice<L> {
             return Err(UsbError::InvalidState);
         }
 
-        usb.uenum.write(|w| w.bits(endpoint_index));
+        usb.uenum.write(|w| w.bits(endpoint_index as u8));
 
-        if usb.uenum.read().bits() & 7 /* 0b111 */ != endpoint_index {
+        if usb.uenum.read().bits() & UENUM_MASK != endpoint_index as u8 {
             return Err(UsbError::InvalidEndpoint);
         }