diff --git a/arch/powerpc/kernel/prom_parse.c b/arch/powerpc/kernel/prom_parse.c
index 21009b1f7869808ef3f6d1befb63416a3d2452bf..6a7e997c401d8ea81cbbf5e3259927c0875000c5 100644
--- a/arch/powerpc/kernel/prom_parse.c
+++ b/arch/powerpc/kernel/prom_parse.c
@@ -881,7 +881,7 @@ int of_irq_map_one(struct device_node *device, int index, struct of_irq *out_irq
 	intsize = *tmp;
 
 	/* Check index */
-	if (index * intsize >= intlen)
+	if ((index + 1) * intsize > intlen)
 		return -EINVAL;
 
 	/* Get new specifier and map it */