diff --git a/OvmfPkg/AmdSevDxe/AmdSevDxe.c b/OvmfPkg/AmdSevDxe/AmdSevDxe.c
index 5955866178..689bfb376d 100644
--- a/OvmfPkg/AmdSevDxe/AmdSevDxe.c
+++ b/OvmfPkg/AmdSevDxe/AmdSevDxe.c
@@ -4,12 +4,13 @@
   in APRIORI. It clears C-bit from MMIO and NonExistent Memory space when SEV
   is enabled.
 
-  Copyright (c) 2017, AMD Inc. All rights reserved.<BR>
+  Copyright (c) 2017 - 2020, AMD Inc. All rights reserved.<BR>
 
   SPDX-License-Identifier: BSD-2-Clause-Patent
 
 **/
 
+#include <IndustryStandard/Q35MchIch9.h>
 #include <Library/BaseLib.h>
 #include <Library/BaseMemoryLib.h>
 #include <Library/DebugLib.h>
@@ -65,6 +66,23 @@ AmdSevDxeEntryPoint (
     FreePool (AllDescMap);
   }
 
+  //
+  // If PCI Express is enabled, the MMCONFIG area has been reserved, rather
+  // than marked as MMIO, and so the C-bit won't be cleared by the above walk
+  // through the GCD map. Check for the MMCONFIG area and clear the C-bit for
+  // the range.
+  //
+  if (PcdGet16 (PcdOvmfHostBridgePciDevId) == INTEL_Q35_MCH_DEVICE_ID) {
+    Status = MemEncryptSevClearPageEncMask (
+               0,
+               FixedPcdGet64 (PcdPciExpressBaseAddress),
+               EFI_SIZE_TO_PAGES (SIZE_256MB),
+               FALSE
+               );
+
+    ASSERT_EFI_ERROR (Status);
+  }
+
   //
   // When SMM is enabled, clear the C-bit from SMM Saved State Area
   //
diff --git a/OvmfPkg/AmdSevDxe/AmdSevDxe.inf b/OvmfPkg/AmdSevDxe/AmdSevDxe.inf
index dd9ecc789a..0676fcc5b6 100644
--- a/OvmfPkg/AmdSevDxe/AmdSevDxe.inf
+++ b/OvmfPkg/AmdSevDxe/AmdSevDxe.inf
@@ -2,7 +2,7 @@
 #
 #  Driver clears the encryption attribute from MMIO regions when SEV is enabled
 #
-#  Copyright (c) 2017, AMD Inc. All rights reserved.<BR>
+#  Copyright (c) 2017 - 2020, AMD Inc. All rights reserved.<BR>
 #
 #  SPDX-License-Identifier: BSD-2-Clause-Patent
 #
@@ -39,3 +39,9 @@
 
 [FeaturePcd]
   gUefiOvmfPkgTokenSpaceGuid.PcdSmmSmramRequire
+
+[FixedPcd]
+  gEfiMdePkgTokenSpaceGuid.PcdPciExpressBaseAddress
+
+[Pcd]
+  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfHostBridgePciDevId