diff --git a/MdePkg/Library/BasePrintLib/PrintLibInternal.c b/MdePkg/Library/BasePrintLib/PrintLibInternal.c
index e7e2964d4f..6ed034615a 100644
--- a/MdePkg/Library/BasePrintLib/PrintLibInternal.c
+++ b/MdePkg/Library/BasePrintLib/PrintLibInternal.c
@@ -911,6 +911,7 @@ BasePrintLibSPrintMarker (
 
 **/
 UINTN
+EFIAPI
 BasePrintLibSPrint (
   OUT CHAR8        *StartOfBuffer,
   IN  UINTN        BufferSize,
diff --git a/MdePkg/Library/BasePrintLib/PrintLibInternal.h b/MdePkg/Library/BasePrintLib/PrintLibInternal.h
index 4c1658a1ce..52ac6d8d5f 100644
--- a/MdePkg/Library/BasePrintLib/PrintLibInternal.h
+++ b/MdePkg/Library/BasePrintLib/PrintLibInternal.h
@@ -102,6 +102,7 @@ BasePrintLibSPrintMarker (
 
 **/
 UINTN
+EFIAPI
 BasePrintLibSPrint (
   OUT CHAR8        *StartOfBuffer,
   IN  UINTN        BufferSize,