diff --git a/MdePkg/Library/DxeHstiLib/HstiDxe.c b/MdePkg/Library/DxeHstiLib/HstiDxe.c
index 58510766bb..d08d8def0c 100644
--- a/MdePkg/Library/DxeHstiLib/HstiDxe.c
+++ b/MdePkg/Library/DxeHstiLib/HstiDxe.c
@@ -1,6 +1,6 @@
 /** @file
 
-  Copyright (c) 2015 - 2017, Intel Corporation. All rights reserved.<BR>
+  Copyright (c) 2015 - 2018, Intel Corporation. All rights reserved.<BR>
   This program and the accompanying materials
   are licensed and made available under the terms and conditions of the BSD License
   which accompanies this distribution.  The full text of the license may be found at
@@ -211,7 +211,7 @@ InternalHstiIsValidTable (
   }
 
   ErrorStringSize = HstiSize - sizeof(ADAPTER_INFO_PLATFORM_SECURITY) - Hsti->SecurityFeaturesSize * 3;
-  ErrorString = (CHAR16 *)((UINTN)Hsti + sizeof(ADAPTER_INFO_PLATFORM_SECURITY) - Hsti->SecurityFeaturesSize * 3);
+  ErrorString = (CHAR16 *)((UINTN)Hsti + sizeof(ADAPTER_INFO_PLATFORM_SECURITY) + Hsti->SecurityFeaturesSize * 3);
 
   //
   // basic check for ErrorString