diff --git a/MdePkg/Library/BasePrintLib/PrintLibInternal.c b/MdePkg/Library/BasePrintLib/PrintLibInternal.c
index cec5b3bc99..28d946472f 100644
--- a/MdePkg/Library/BasePrintLib/PrintLibInternal.c
+++ b/MdePkg/Library/BasePrintLib/PrintLibInternal.c
@@ -1165,7 +1165,7 @@ BasePrintLibSPrintMarker (
     // Copy the string into the output buffer performing the required type conversions
     //
     while (Index < Count) {
-      ArgumentCharacter = ((*ArgumentString & 0xff) | (*(ArgumentString + 1) << 8)) & ArgumentMask;
+      ArgumentCharacter = ((*ArgumentString & 0xff) | (((UINT8)*(ArgumentString + 1)) << 8)) & ArgumentMask;
 
       LengthToReturn += (1 * BytesPerOutputCharacter);
       if ((Flags & COUNT_ONLY_NO_PRINT) == 0 && Buffer != NULL) {