diff --git a/MdePkg/Include/Library/UefiRuntimeLib.h b/MdePkg/Include/Library/UefiRuntimeLib.h
index 396dc781d0..af3aaf40ce 100644
--- a/MdePkg/Include/Library/UefiRuntimeLib.h
+++ b/MdePkg/Include/Library/UefiRuntimeLib.h
@@ -333,7 +333,7 @@ EFIAPI
 EfiUpdateCapsule (
   IN EFI_CAPSULE_HEADER       **CapsuleHeaderArray,
   IN UINTN                    CapsuleCount,
-  IN EFI_PHYSICAL_ADDRESS     ScatterGatherList
+  IN EFI_PHYSICAL_ADDRESS     ScatterGatherList OPTIONAL
   );