diff --git a/MdePkg/Library/UefiDebugLibConOut/DebugLib.c b/MdePkg/Library/UefiDebugLibConOut/DebugLib.c
index c430419c99..cf168d05cf 100644
--- a/MdePkg/Library/UefiDebugLibConOut/DebugLib.c
+++ b/MdePkg/Library/UefiDebugLibConOut/DebugLib.c
@@ -9,7 +9,6 @@
 #include <Uefi.h>
 
 #include <Library/DebugLib.h>
-#include <Library/UefiBootServicesTableLib.h>
 #include <Library/PrintLib.h>
 #include <Library/PcdLib.h>
 #include <Library/BaseLib.h>
@@ -27,6 +26,9 @@
 //
 VA_LIST     mVaListNull;
 
+extern BOOLEAN                mPostEBS;
+extern EFI_SYSTEM_TABLE       *mDebugST;
+
 /**
   Prints a debug message to the debug output device if the specified error level is enabled.
 
@@ -85,33 +87,35 @@ DebugPrintMarker (
 {
   CHAR16   Buffer[MAX_DEBUG_MESSAGE_LENGTH];
 
-  //
-  // If Format is NULL, then ASSERT().
-  //
-  ASSERT (Format != NULL);
+  if (!mPostEBS) {
+    //
+    // If Format is NULL, then ASSERT().
+    //
+    ASSERT (Format != NULL);
 
-  //
-  // Check driver debug mask value and global mask
-  //
-  if ((ErrorLevel & GetDebugPrintErrorLevel ()) == 0) {
-    return;
-  }
+    //
+    // Check driver debug mask value and global mask
+    //
+    if ((ErrorLevel & GetDebugPrintErrorLevel ()) == 0) {
+      return;
+    }
 
-  //
-  // Convert the DEBUG() message to a Unicode String
-  //
-  if (BaseListMarker == NULL) {
-    UnicodeVSPrintAsciiFormat (Buffer, MAX_DEBUG_MESSAGE_LENGTH,  Format, VaListMarker);
-  } else {
-    UnicodeBSPrintAsciiFormat (Buffer, MAX_DEBUG_MESSAGE_LENGTH,  Format, BaseListMarker);
-  }
+    //
+    // Convert the DEBUG() message to a Unicode String
+    //
+    if (BaseListMarker == NULL) {
+      UnicodeVSPrintAsciiFormat (Buffer, MAX_DEBUG_MESSAGE_LENGTH,  Format, VaListMarker);
+    } else {
+      UnicodeBSPrintAsciiFormat (Buffer, MAX_DEBUG_MESSAGE_LENGTH,  Format, BaseListMarker);
+    }
 
 
-  //
-  // Send the print string to the Console Output device
-  //
-  if ((gST != NULL) && (gST->ConOut != NULL)) {
-    gST->ConOut->OutputString (gST->ConOut, Buffer);
+    //
+    // Send the print string to the Console Output device
+    //
+    if ((mDebugST != NULL) && (mDebugST->ConOut != NULL)) {
+      mDebugST->ConOut->OutputString (mDebugST->ConOut, Buffer);
+    }
   }
 }
 
@@ -205,33 +209,35 @@ DebugAssert (
 {
   CHAR16  Buffer[MAX_DEBUG_MESSAGE_LENGTH];
 
-  //
-  // Generate the ASSERT() message in Unicode format
-  //
-  UnicodeSPrintAsciiFormat (
-    Buffer,
-    sizeof (Buffer),
-    "ASSERT [%a] %a(%d): %a\n",
-    gEfiCallerBaseName,
-    FileName,
-    LineNumber,
-    Description
-    );
+  if (!mPostEBS) {
+    //
+    // Generate the ASSERT() message in Unicode format
+    //
+    UnicodeSPrintAsciiFormat (
+      Buffer,
+      sizeof (Buffer),
+      "ASSERT [%a] %a(%d): %a\n",
+      gEfiCallerBaseName,
+      FileName,
+      LineNumber,
+      Description
+      );
 
-  //
-  // Send the print string to the Console Output device
-  //
-  if ((gST != NULL) && (gST->ConOut != NULL)) {
-    gST->ConOut->OutputString (gST->ConOut, Buffer);
-  }
+    //
+    // Send the print string to the Console Output device
+    //
+    if ((mDebugST != NULL) && (mDebugST->ConOut != NULL)) {
+      mDebugST->ConOut->OutputString (mDebugST->ConOut, Buffer);
+    }
 
-  //
-  // Generate a Breakpoint, DeadLoop, or NOP based on PCD settings
-  //
-  if ((PcdGet8(PcdDebugPropertyMask) & DEBUG_PROPERTY_ASSERT_BREAKPOINT_ENABLED) != 0) {
-    CpuBreakpoint ();
-  } else if ((PcdGet8(PcdDebugPropertyMask) & DEBUG_PROPERTY_ASSERT_DEADLOOP_ENABLED) != 0) {
-    CpuDeadLoop ();
+    //
+    // Generate a Breakpoint, DeadLoop, or NOP based on PCD settings
+    //
+    if ((PcdGet8(PcdDebugPropertyMask) & DEBUG_PROPERTY_ASSERT_BREAKPOINT_ENABLED) != 0) {
+      CpuBreakpoint ();
+    } else if ((PcdGet8(PcdDebugPropertyMask) & DEBUG_PROPERTY_ASSERT_DEADLOOP_ENABLED) != 0) {
+      CpuDeadLoop ();
+    }
   }
 }
 
diff --git a/MdePkg/Library/UefiDebugLibConOut/DebugLibConstructor.c b/MdePkg/Library/UefiDebugLibConOut/DebugLibConstructor.c
new file mode 100644
index 0000000000..d4fdfbab55
--- /dev/null
+++ b/MdePkg/Library/UefiDebugLibConOut/DebugLibConstructor.c
@@ -0,0 +1,77 @@
+/** @file
+  UEFI Dxe DebugLib constructor that prevent some debug service after ExitBootServices event,
+  because some pointer is nulled at that phase.
+
+  Copyright (c) 2018, Microsoft Corporation
+  Copyright (c) 2015 - 2019, Intel Corporation. All rights reserved.<BR>
+
+  SPDX-License-Identifier: BSD-2-Clause-Patent
+**/
+
+#include <Uefi.h>
+#include <Library/BaseLib.h>
+#include <Library/BaseMemoryLib.h>
+
+//
+// BOOLEAN value to indicate if it is at the post ExitBootServices pahse
+//
+BOOLEAN     mPostEBS = FALSE;
+
+EFI_EVENT   mExitBootServicesEvent;
+
+//
+// Pointer to SystemTable
+// This library instance may have a cycle consume with UefiBootServicesTableLib
+// because of the constructors.
+//
+EFI_SYSTEM_TABLE      *mDebugST;
+
+/**
+  This routine sets the mPostEBS for exit boot servies true
+  to prevent DebugPort protocol dereferences when the pointer is nulled.
+
+  @param  Event        Event whose notification function is being invoked.
+  @param  Context      Pointer to the notification function's context.
+
+**/
+VOID
+EFIAPI
+ExitBootServicesCallback (
+  EFI_EVENT   Event,
+  VOID*       Context
+  )
+{
+  mPostEBS = TRUE;
+  return;
+}
+
+/**
+  The constructor gets the pointers to the system table.
+  And create a event to indicate it is after ExitBootServices.
+
+  @param  ImageHandle     The firmware allocated handle for the EFI image.
+  @param  SystemTable     A pointer to the EFI System Table.
+
+  @retval EFI_SUCCESS     The constructor always returns EFI_SUCCESS.
+
+**/
+EFI_STATUS
+EFIAPI
+DxeDebugLibConstructor(
+  IN EFI_HANDLE                 ImageHandle,
+  IN EFI_SYSTEM_TABLE           *SystemTable
+  )
+{
+  mDebugST = SystemTable;
+
+  SystemTable->BootServices->CreateEventEx (
+                                EVT_NOTIFY_SIGNAL,
+                                TPL_NOTIFY,
+                                ExitBootServicesCallback,
+                                NULL,
+                                &gEfiEventExitBootServicesGuid,
+                                &mExitBootServicesEvent
+                                );
+
+  return EFI_SUCCESS;
+}
diff --git a/MdePkg/Library/UefiDebugLibConOut/UefiDebugLibConOut.inf b/MdePkg/Library/UefiDebugLibConOut/UefiDebugLibConOut.inf
index 12af4a9e98..4c279a5bf2 100644
--- a/MdePkg/Library/UefiDebugLibConOut/UefiDebugLibConOut.inf
+++ b/MdePkg/Library/UefiDebugLibConOut/UefiDebugLibConOut.inf
@@ -3,7 +3,9 @@
 #
 #  Debug Lib that sends messages to the Console Output Device in the EFI System Table.
 #
-#  Copyright (c) 2007 - 2018, Intel Corporation. All rights reserved.<BR>
+#  Copyright (c) 2018, Microsoft Corporation
+#
+#  Copyright (c) 2007 - 2019, Intel Corporation. All rights reserved.<BR>
 #
 #  SPDX-License-Identifier: BSD-2-Clause-Patent
 #
@@ -17,8 +19,9 @@
   FILE_GUID                      = 5cddfaf3-e9a7-4d16-bdce-1e002df475bb
   MODULE_TYPE                    = UEFI_DRIVER
   VERSION_STRING                 = 1.0
-  LIBRARY_CLASS                  = DebugLib|DXE_CORE DXE_DRIVER DXE_RUNTIME_DRIVER DXE_SMM_DRIVER UEFI_APPLICATION UEFI_DRIVER
+  LIBRARY_CLASS                  = DebugLib|DXE_CORE DXE_DRIVER DXE_RUNTIME_DRIVER UEFI_APPLICATION UEFI_DRIVER
 
+  CONSTRUCTOR                    = DxeDebugLibConstructor
 
 #
 #  VALID_ARCHITECTURES           = IA32 X64 EBC
@@ -27,6 +30,7 @@
 
 [Sources]
   DebugLib.c
+  DebugLibConstructor.c
 
 
 
@@ -39,9 +43,11 @@
   BaseLib
   PcdLib
   PrintLib
-  UefiBootServicesTableLib
   DebugPrintErrorLevelLib
 
+[Guids]
+  gEfiEventExitBootServicesGuid                 ## CONSUMES
+
 [Pcd]
   gEfiMdePkgTokenSpaceGuid.PcdDebugClearMemoryValue        ## SOMETIMES_CONSUMES
   gEfiMdePkgTokenSpaceGuid.PcdDebugPropertyMask            ## CONSUMES