diff --git a/MdePkg/Include/Library/PciSegmentInfoLib.h b/MdePkg/Include/Library/PciSegmentInfoLib.h
index 320a2236286e..659ff856497c 100644
--- a/MdePkg/Include/Library/PciSegmentInfoLib.h
+++ b/MdePkg/Include/Library/PciSegmentInfoLib.h
@@ -3,7 +3,7 @@
 
   This library is consumed by PciSegmentLib to support multiple segment PCI configuration access.
 
-  Copyright (c) 2017, Intel Corporation. All rights reserved.<BR>
+  Copyright (c) 2017 - 2020, Intel Corporation. All rights reserved.<BR>
   SPDX-License-Identifier: BSD-2-Clause-Patent
 
 **/
@@ -28,6 +28,7 @@ typedef struct {
   @retval A callee owned array holding the segment information.
 **/
 PCI_SEGMENT_INFO *
+EFIAPI
 GetPciSegmentInfo (
   UINTN  *Count
   );
diff --git a/MdePkg/Library/BasePciSegmentInfoLibNull/PciSegmentInfoLib.c b/MdePkg/Library/BasePciSegmentInfoLibNull/PciSegmentInfoLib.c
index f9019c4e6461..3ec77840570a 100644
--- a/MdePkg/Library/BasePciSegmentInfoLibNull/PciSegmentInfoLib.c
+++ b/MdePkg/Library/BasePciSegmentInfoLibNull/PciSegmentInfoLib.c
@@ -2,7 +2,7 @@
   Default PCI Segment Information Library that returns one segment whose
   segment base address equals to PcdPciExpressBaseAddress.
 
-  Copyright (c) 2017, Intel Corporation. All rights reserved.<BR>
+  Copyright (c) 2017 - 2020, Intel Corporation. All rights reserved.<BR>
   SPDX-License-Identifier: BSD-2-Clause-Patent
 
 **/
@@ -21,6 +21,7 @@
   @retval A callee owned array holding the segment information.
 **/
 PCI_SEGMENT_INFO *
+EFIAPI
 GetPciSegmentInfo (
   UINTN  *Count
   )