diff --git a/psx/src/hw/irq.rs b/psx/src/hw/irq.rs
index 319490f..1c58659 100644
--- a/psx/src/hw/irq.rs
+++ b/psx/src/hw/irq.rs
@@ -1,14 +1,12 @@
 //! Interrupt request and acknowledge
 use crate::hw::{MemRegister, Register};
-use crate::irq::{ALL_IRQS, IRQ};
-use core::mem::variant_count;
+use crate::irq::{ALL_IRQS, IRQ, NUM_IRQS};
 
 /// Interrupt status register
 pub type Status = MemRegister<u16, 0x1F80_1070>;
 /// Interrupt mask register
 pub type Mask = MemRegister<u16, 0x1F80_1074>;
 
-const NUM_IRQS: usize = variant_count::<IRQ>();
 const ALL_IRQS_BITS: u16 = (1 << NUM_IRQS) - 1;
 
 impl Status {
diff --git a/psx/src/lib.rs b/psx/src/lib.rs
index be1e90b..e2a9629 100644
--- a/psx/src/lib.rs
+++ b/psx/src/lib.rs
@@ -128,7 +128,13 @@ pub mod constants {
 
 /// Interrupt request types
 pub mod irq {
+    use core::mem::variant_count;
+
+    /// The number of different interrupt requests
+    pub const NUM_IRQS: usize = variant_count::<IRQ>();
+
     /// An interrupt request
+    #[repr(u16)]
     #[derive(Clone, Copy, Debug, PartialEq, Eq)]
     pub enum IRQ {
         /// vertical blank interrupt request (NTSC = 60Hz, PAL = 50Hz)