diff --git a/MdePkg/Include/Library/PeiServicesLib.h b/MdePkg/Include/Library/PeiServicesLib.h
index 0be72237f2..7cea34000c 100644
--- a/MdePkg/Include/Library/PeiServicesLib.h
+++ b/MdePkg/Include/Library/PeiServicesLib.h
@@ -1,7 +1,7 @@
 /** @file
   Provides library functions for all PEI Services.
 
-Copyright (c) 2006 - 2017, Intel Corporation. All rights reserved.<BR>
+Copyright (c) 2006 - 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
@@ -73,7 +73,7 @@ EFIAPI
 PeiServicesLocatePpi (
   IN CONST EFI_GUID                   *Guid,
   IN UINTN                      Instance,
-  IN OUT EFI_PEI_PPI_DESCRIPTOR **PpiDescriptor,
+  IN OUT EFI_PEI_PPI_DESCRIPTOR **PpiDescriptor, OPTIONAL
   IN OUT VOID                   **Ppi
   );
 
diff --git a/MdePkg/Library/PeiServicesLib/PeiServicesLib.c b/MdePkg/Library/PeiServicesLib/PeiServicesLib.c
index d0838ed709..881b9cd52e 100644
--- a/MdePkg/Library/PeiServicesLib/PeiServicesLib.c
+++ b/MdePkg/Library/PeiServicesLib/PeiServicesLib.c
@@ -1,7 +1,7 @@
 /** @file
   Implementation for PEI Services Library.
 
-  Copyright (c) 2006 - 2017, Intel Corporation. All rights reserved.<BR>
+  Copyright (c) 2006 - 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
@@ -95,7 +95,7 @@ EFIAPI
 PeiServicesLocatePpi (
   IN CONST EFI_GUID                   *Guid,
   IN UINTN                      Instance,
-  IN OUT EFI_PEI_PPI_DESCRIPTOR **PpiDescriptor,
+  IN OUT EFI_PEI_PPI_DESCRIPTOR **PpiDescriptor, OPTIONAL
   IN OUT VOID                   **Ppi
   )
 {