diff --git a/MdePkg/Library/HiiLib/HiiLib.c b/MdePkg/Library/HiiLib/HiiLib.c
index 29899f5d8c..975a064a39 100644
--- a/MdePkg/Library/HiiLib/HiiLib.c
+++ b/MdePkg/Library/HiiLib/HiiLib.c
@@ -615,7 +615,7 @@ EFIAPI
 HiiLibListPackageLists (
   IN        UINT8                     PackageType,
   IN CONST  EFI_GUID                  *PackageGuid,
-  OUT    UINTN                        *HandleBufferLength,
+  IN OUT    UINTN                     *HandleBufferLength,
   OUT       EFI_HII_HANDLE            **HandleBuffer
   )
 {