diff --git a/MdePkg/Include/Library/PeiServicesLib.h b/MdePkg/Include/Library/PeiServicesLib.h
index 193d6bad8c..e417870cdb 100644
--- a/MdePkg/Include/Library/PeiServicesLib.h
+++ b/MdePkg/Include/Library/PeiServicesLib.h
@@ -109,7 +109,7 @@ PeiServicesNotifyPpi (
 EFI_STATUS
 EFIAPI
 PeiServicesGetBootMode (
-  IN OUT EFI_BOOT_MODE          *BootMode
+  OUT EFI_BOOT_MODE          *BootMode
   );
 
 /**
diff --git a/MdePkg/Library/PeiServicesLib/PeiServicesLib.c b/MdePkg/Library/PeiServicesLib/PeiServicesLib.c
index da872e8284..a2ce52dcd2 100644
--- a/MdePkg/Library/PeiServicesLib/PeiServicesLib.c
+++ b/MdePkg/Library/PeiServicesLib/PeiServicesLib.c
@@ -151,7 +151,7 @@ PeiServicesNotifyPpi (
 EFI_STATUS
 EFIAPI
 PeiServicesGetBootMode (
-  IN OUT EFI_BOOT_MODE          *BootMode
+  OUT EFI_BOOT_MODE          *BootMode
   )
 {
   CONST EFI_PEI_SERVICES **PeiServices;