diff --git a/ports/arm/atomport-private.h b/ports/arm/atomport-private.h
index 35f1a80..f2c7981 100644
--- a/ports/arm/atomport-private.h
+++ b/ports/arm/atomport-private.h
@@ -30,12 +30,8 @@
 #ifndef __ATOM_PORT_PRIVATE_H
 #define __ATOM_PORT_PRIVATE_H
 
-/* ISR handler prototype used for registration of interuppt handlers */
-typedef void (*ISR_FUNC)(void);
-
 /* Function prototypes */
 extern void archIRQHandler (void);
-extern int archISRInstall (int int_vector, ISR_FUNC isr_func);
 
 /* Platform-specific interrupt dispatcher called on receipt of IRQ */
 extern void __interrupt_dispatcher (void);
diff --git a/ports/arm/atomport.h b/ports/arm/atomport.h
index 9f0f363..c2d5378 100644
--- a/ports/arm/atomport.h
+++ b/ports/arm/atomport.h
@@ -56,6 +56,12 @@ extern void archUsleep (int32_t microsecs);
 extern int32_t archUsleepStart (void);
 extern int archUsleepCheckExpired (int32_t start_time, int32_t delay_usecs);
 
+/**
+ * ISR handler registration (optional, not available on all ports)
+ */
+typedef void (*ISR_FUNC)(void);
+extern int archISRInstall (int int_vector, ISR_FUNC isr_func);
+
 /**
  *
  * Functions defined in atomport_arm.asm