diff --git a/UefiCpuPkg/Include/Library/MtrrLib.h b/UefiCpuPkg/Include/Library/MtrrLib.h
index 66e131d4fd..b34384b14c 100644
--- a/UefiCpuPkg/Include/Library/MtrrLib.h
+++ b/UefiCpuPkg/Include/Library/MtrrLib.h
@@ -135,6 +135,7 @@ typedef enum {
 
 **/
 UINT32
+EFIAPI
 GetVariableMtrrCount (
   VOID
   );
@@ -146,6 +147,7 @@ GetVariableMtrrCount (
 
 **/
 UINT32
+EFIAPI
 GetFirmwareVariableMtrrCount (
   VOID
   );
@@ -311,6 +313,7 @@ MtrrGetMemoryAttributeInVariableMtrr (
   This function prints all MTRRs for debugging.
 **/
 VOID
+EFIAPI
 MtrrDebugPrintAllMtrrs (
   );
 
@@ -322,6 +325,7 @@ MtrrDebugPrintAllMtrrs (
 
 **/
 BOOLEAN
+EFIAPI
 IsMtrrSupported (
   VOID
   );
diff --git a/UefiCpuPkg/Library/MtrrLib/MtrrLib.c b/UefiCpuPkg/Library/MtrrLib/MtrrLib.c
index dab0535fe9..d48b6a4db3 100644
--- a/UefiCpuPkg/Library/MtrrLib/MtrrLib.c
+++ b/UefiCpuPkg/Library/MtrrLib/MtrrLib.c
@@ -89,6 +89,7 @@ FIXED_MTRR    MtrrLibFixedMtrrTable[] = {
 
 **/
 UINT32
+EFIAPI
 GetVariableMtrrCount (
   VOID
   )
@@ -107,6 +108,7 @@ GetVariableMtrrCount (
 
 **/
 UINT32
+EFIAPI
 GetFirmwareVariableMtrrCount (
   VOID
   )