diff --git a/MdePkg/Library/BaseMemoryLib/MemLibInternals.h b/MdePkg/Library/BaseMemoryLib/MemLibInternals.h
index 6781fe844e..fec91f270f 100644
--- a/MdePkg/Library/BaseMemoryLib/MemLibInternals.h
+++ b/MdePkg/Library/BaseMemoryLib/MemLibInternals.h
@@ -62,7 +62,7 @@ InternalMemCopyMem (
 VOID *
 EFIAPI
 InternalMemSetMem (
-  OUT     VOID                      *Buffer,
+  IN      VOID                      *Buffer,
   IN      UINTN                     Length,
   IN      UINT8                     Value
   );
diff --git a/MdePkg/Library/BaseMemoryLib/SetMem.c b/MdePkg/Library/BaseMemoryLib/SetMem.c
index a4f783fde6..69fa265ba2 100644
--- a/MdePkg/Library/BaseMemoryLib/SetMem.c
+++ b/MdePkg/Library/BaseMemoryLib/SetMem.c
@@ -24,7 +24,7 @@
   Set Buffer to Value for Size bytes.
 
   @param  Buffer Memory to set.
-  @param  Size Number of bytes to set
+  @param  Length Number of bytes to set
   @param  Value Value of the set operation.
 
   @return Buffer
@@ -34,7 +34,7 @@ VOID *
 EFIAPI
 InternalMemSetMem (
   IN      VOID                      *Buffer,
-  IN      UINTN                     Size,
+  IN      UINTN                     Length,
   IN      UINT8                     Value
   )
 {