diff --git a/drivers/pci/dmar.c b/drivers/pci/dmar.c
index 380b60e..3264b62 100644
--- a/drivers/pci/dmar.c
+++ b/drivers/pci/dmar.c
@@ -1226,7 +1226,7 @@
 				source_id, guest_addr);
 
 		fault_index++;
-		if (fault_index > cap_num_fault_regs(iommu->cap))
+		if (fault_index >= cap_num_fault_regs(iommu->cap))
 			fault_index = 0;
 		spin_lock_irqsave(&iommu->register_lock, flag);
 	}