diff --git a/drivers/pci/intel-iommu.c b/drivers/pci/intel-iommu.c
index 585e188..a4c3089 100644
--- a/drivers/pci/intel-iommu.c
+++ b/drivers/pci/intel-iommu.c
@@ -745,7 +745,7 @@
 
 /* iommu interrupt handling. Most stuff are MSI-like. */
 
-static char *fault_reason_strings[] =
+static const char *fault_reason_strings[] =
 {
 	"Software",
 	"Present bit in root entry is clear",
@@ -760,14 +760,13 @@
 	"non-zero reserved fields in RTP",
 	"non-zero reserved fields in CTP",
 	"non-zero reserved fields in PTE",
-	"Unknown"
 };
 #define MAX_FAULT_REASON_IDX 	(ARRAY_SIZE(fault_reason_strings) - 1)
 
-char *dmar_get_fault_reason(u8 fault_reason)
+const char *dmar_get_fault_reason(u8 fault_reason)
 {
-	if (fault_reason >= MAX_FAULT_REASON_IDX)
-		return fault_reason_strings[MAX_FAULT_REASON_IDX - 1];
+	if (fault_reason > MAX_FAULT_REASON_IDX)
+		return "Unknown";
 	else
 		return fault_reason_strings[fault_reason];
 }
@@ -825,7 +824,7 @@
 static int iommu_page_fault_do_one(struct intel_iommu *iommu, int type,
 		u8 fault_reason, u16 source_id, u64 addr)
 {
-	char *reason;
+	const char *reason;
 
 	reason = dmar_get_fault_reason(fault_reason);