diff --git a/20_timer_callbacks/README.md b/20_timer_callbacks/README.md
index 3647fb38..7d944b99 100644
--- a/20_timer_callbacks/README.md
+++ b/20_timer_callbacks/README.md
@@ -58,7 +58,7 @@ diff -uNr 19_kernel_heap/kernel/src/_arch/aarch64/time.rs 20_timer_callbacks/ker
 +
 +/// The associated IRQ number.
 +pub const fn timeout_irq() -> exception::asynchronous::IRQNumber {
-+    bsp::exception::asynchronous::irq_map::ARM_NS_PHYISCAL_TIMER
++    bsp::exception::asynchronous::irq_map::ARM_NS_PHYSICAL_TIMER
 +}
 +
 +/// Program a timer IRQ to be fired after `delay` has passed.
@@ -398,7 +398,7 @@ diff -uNr 19_kernel_heap/kernel/src/bsp/raspberrypi/exception/asynchronous.rs 20
 
 -    pub const PL011_UART: IRQNumber = IRQNumber::Peripheral(PeripheralIRQ::new(57));
 +    /// The non-secure physical timer IRQ number.
-+    pub const ARM_NS_PHYISCAL_TIMER: IRQNumber = IRQNumber::Local(LocalIRQ::new(1));
++    pub const ARM_NS_PHYSICAL_TIMER: IRQNumber = IRQNumber::Local(LocalIRQ::new(1));
 +
 +    pub(in crate::bsp) const PL011_UART: IRQNumber = IRQNumber::Peripheral(PeripheralIRQ::new(57));
  }
@@ -411,7 +411,7 @@ diff -uNr 19_kernel_heap/kernel/src/bsp/raspberrypi/exception/asynchronous.rs 20
 
 -    pub const PL011_UART: IRQNumber = IRQNumber::new(153);
 +    /// The non-secure physical timer IRQ number.
-+    pub const ARM_NS_PHYISCAL_TIMER: IRQNumber = IRQNumber::new(30);
++    pub const ARM_NS_PHYSICAL_TIMER: IRQNumber = IRQNumber::new(30);
 +
 +    pub(in crate::bsp) const PL011_UART: IRQNumber = IRQNumber::new(153);
  }
diff --git a/20_timer_callbacks/kernel/src/_arch/aarch64/time.rs b/20_timer_callbacks/kernel/src/_arch/aarch64/time.rs
index 568363fc..5479deb4 100644
--- a/20_timer_callbacks/kernel/src/_arch/aarch64/time.rs
+++ b/20_timer_callbacks/kernel/src/_arch/aarch64/time.rs
@@ -166,7 +166,7 @@ pub fn spin_for(duration: Duration) {
 
 /// The associated IRQ number.
 pub const fn timeout_irq() -> exception::asynchronous::IRQNumber {
-    bsp::exception::asynchronous::irq_map::ARM_NS_PHYISCAL_TIMER
+    bsp::exception::asynchronous::irq_map::ARM_NS_PHYSICAL_TIMER
 }
 
 /// Program a timer IRQ to be fired after `delay` has passed.
diff --git a/20_timer_callbacks/kernel/src/bsp/raspberrypi/exception/asynchronous.rs b/20_timer_callbacks/kernel/src/bsp/raspberrypi/exception/asynchronous.rs
index a6fd27fb..b2cb955e 100644
--- a/20_timer_callbacks/kernel/src/bsp/raspberrypi/exception/asynchronous.rs
+++ b/20_timer_callbacks/kernel/src/bsp/raspberrypi/exception/asynchronous.rs
@@ -19,7 +19,7 @@ pub mod irq_map {
     use super::bsp::device_driver::{IRQNumber, LocalIRQ, PeripheralIRQ};
 
     /// The non-secure physical timer IRQ number.
-    pub const ARM_NS_PHYISCAL_TIMER: IRQNumber = IRQNumber::Local(LocalIRQ::new(1));
+    pub const ARM_NS_PHYSICAL_TIMER: IRQNumber = IRQNumber::Local(LocalIRQ::new(1));
 
     pub(in crate::bsp) const PL011_UART: IRQNumber = IRQNumber::Peripheral(PeripheralIRQ::new(57));
 }
@@ -30,7 +30,7 @@ pub mod irq_map {
     use super::bsp::device_driver::IRQNumber;
 
     /// The non-secure physical timer IRQ number.
-    pub const ARM_NS_PHYISCAL_TIMER: IRQNumber = IRQNumber::new(30);
+    pub const ARM_NS_PHYSICAL_TIMER: IRQNumber = IRQNumber::new(30);
 
     pub(in crate::bsp) const PL011_UART: IRQNumber = IRQNumber::new(153);
 }