diff --git a/arch/um/include/asm/irq.h b/arch/um/include/asm/irq.h
index 49ed3e35b35a..ce7a78c3bcf2 100644
--- a/arch/um/include/asm/irq.h
+++ b/arch/um/include/asm/irq.h
@@ -23,7 +23,7 @@
 #define VECTOR_BASE_IRQ		15
 #define VECTOR_IRQ_SPACE	8
 
-#define LAST_IRQ (VECTOR_IRQ_SPACE + VECTOR_BASE_IRQ)
+#define LAST_IRQ (VECTOR_IRQ_SPACE + VECTOR_BASE_IRQ - 1)
 
 #else