diff --git a/UefiCpuPkg/Include/Library/MtrrLib.h b/UefiCpuPkg/Include/Library/MtrrLib.h
index 0bf7d8ed10..d56f1057e1 100644
--- a/UefiCpuPkg/Include/Library/MtrrLib.h
+++ b/UefiCpuPkg/Include/Library/MtrrLib.h
@@ -1,7 +1,7 @@
 /** @file
   MTRR setting library
 
-  Copyright (c) 2008 - 2017, Intel Corporation. All rights reserved.<BR>
+  Copyright (c) 2008 - 2018, Intel Corporation. All rights reserved.<BR>
   This program and the accompanying materials
   are licensed and made available under the terms and conditions of the BSD License
   which accompanies this distribution.  The full text of the license may be found at
@@ -157,7 +157,9 @@ GetFirmwareVariableMtrrCount (
   @retval RETURN_OUT_OF_RESOURCES   There are not enough system resources to
                                     modify the attributes of the memory
                                     resource range.
-  @retval RETURN_BUFFER_TOO_SMALL   The scratch buffer is too small for MTRR calculation.
+  @retval RETURN_BUFFER_TOO_SMALL   The fixed internal scratch buffer is too small for MTRR calculation.
+                                    Caller should use MtrrSetMemoryAttributesInMtrrSettings() to specify
+                                    external scratch buffer.
 **/
 RETURN_STATUS
 EFIAPI
@@ -352,7 +354,9 @@ MtrrGetDefaultMemoryType (
                                     BaseAddress and Length cannot be modified.
   @retval RETURN_OUT_OF_RESOURCES   There are not enough system resources to modify the attributes of
                                     the memory resource range.
-  @retval RETURN_BUFFER_TOO_SMALL   The scratch buffer is too small for MTRR calculation.
+  @retval RETURN_BUFFER_TOO_SMALL   The fixed internal scratch buffer is too small for MTRR calculation.
+                                    Caller should use MtrrSetMemoryAttributesInMtrrSettings() to specify
+                                    external scratch buffer.
 **/
 RETURN_STATUS
 EFIAPI
diff --git a/UefiCpuPkg/Library/MtrrLib/MtrrLib.c b/UefiCpuPkg/Library/MtrrLib/MtrrLib.c
index 30b0df030b..2496d08ad4 100644
--- a/UefiCpuPkg/Library/MtrrLib/MtrrLib.c
+++ b/UefiCpuPkg/Library/MtrrLib/MtrrLib.c
@@ -2513,7 +2513,9 @@ Exit:
                                     BaseAddress and Length cannot be modified.
   @retval RETURN_OUT_OF_RESOURCES   There are not enough system resources to modify the attributes of
                                     the memory resource range.
-  @retval RETURN_BUFFER_TOO_SMALL   The scratch buffer is too small for MTRR calculation.
+  @retval RETURN_BUFFER_TOO_SMALL   The fixed internal scratch buffer is too small for MTRR calculation.
+                                    Caller should use MtrrSetMemoryAttributesInMtrrSettings() to specify
+                                    external scratch buffer.
 **/
 RETURN_STATUS
 EFIAPI
@@ -2559,7 +2561,9 @@ MtrrSetMemoryAttributeInMtrrSettings (
   @retval RETURN_OUT_OF_RESOURCES   There are not enough system resources to
                                     modify the attributes of the memory
                                     resource range.
-  @retval RETURN_BUFFER_TOO_SMALL   The scratch buffer is too small for MTRR calculation.
+  @retval RETURN_BUFFER_TOO_SMALL   The fixed internal scratch buffer is too small for MTRR calculation.
+                                    Caller should use MtrrSetMemoryAttributesInMtrrSettings() to specify
+                                    external scratch buffer.
 **/
 RETURN_STATUS
 EFIAPI