--- a/sys/platform/pc64/icu/icu.c
+++ b/sys/platform/pc64/icu/icu.c
@@ -163,7 +163,7 @@ int
 icu_ioapic_extint(int irq, int vec)
 {
 	uint8_t mask;
 
 	/*
 	 * Only first 8 interrupt is supported.
 	 * Don't allow setup for the slave link.
 	 */
-	if (irq >= 8 || irq == 2)
+	if (irq < 0 || irq >= 8 || irq == 2)
 		return EOPNOTSUPP;
 
 	mask = ~(1 << irq);