diff --git a/include/arch/arm/arch/machine/registerset.h b/include/arch/arm/arch/machine/registerset.h
index 21bc114..138dad4 100644
--- a/include/arch/arm/arch/machine/registerset.h
+++ b/include/arch/arm/arch/machine/registerset.h
@@ -33,6 +36,10 @@
                              | PMODE_SUPERVISOR   \
                              | CPSR_EXTRA_FLAGS   )
 
+#define CPSR_IDLETHREAD      ( PMASK_FIRQ         \
+                             | PMODE_SUPERVISOR   \
+                             | CPSR_EXTRA_FLAGS   )
+
 #ifdef __ASSEMBLER__
 
 /* Offsets within the user context, these need to match the order in
diff --git a/src/arch/arm/kernel/thread.c b/src/arch/arm/kernel/thread.c
index ee88fce..a9af577 100644
--- a/src/arch/arm/kernel/thread.c
+++ b/src/arch/arm/kernel/thread.c
@@ -26,7 +26,7 @@ Arch_switchToThread(tcb_t *tcb)
 BOOT_CODE void
 Arch_configureIdleThread(tcb_t *tcb)
 {
-    setRegister(tcb, CPSR, 0x1f);
+    setRegister(tcb, CPSR, CPSR_IDLETHREAD);
     setRegister(tcb, LR_svc, (word_t)idleThreadStart);
 }