diff --git a/MdeModulePkg/Bus/Pci/PciBusDxe/PciEnumeratorSupport.c b/MdeModulePkg/Bus/Pci/PciBusDxe/PciEnumeratorSupport.c
index 620933779c..ccec37b287 100644
--- a/MdeModulePkg/Bus/Pci/PciBusDxe/PciEnumeratorSupport.c
+++ b/MdeModulePkg/Bus/Pci/PciBusDxe/PciEnumeratorSupport.c
@@ -1130,8 +1130,12 @@ DetermineDeviceAttribute (
     if (EFI_ERROR (Status)) {
       return Status;
     }
+    //
+    // Assume the PCI Root Bridge supports DAC
+    //
     PciIoDevice->Supports |= (EFI_PCI_IO_ATTRIBUTE_EMBEDDED_DEVICE |
-                              EFI_PCI_IO_ATTRIBUTE_EMBEDDED_ROM);
+                              EFI_PCI_IO_ATTRIBUTE_EMBEDDED_ROM |
+                              EFI_PCI_IO_ATTRIBUTE_DUAL_ADDRESS_CYCLE);
 
   } else {
 
diff --git a/MdeModulePkg/Bus/Pci/PciBusDxe/PciIo.c b/MdeModulePkg/Bus/Pci/PciBusDxe/PciIo.c
index e4bde1ebe9..64f1f1b7c8 100644
--- a/MdeModulePkg/Bus/Pci/PciBusDxe/PciIo.c
+++ b/MdeModulePkg/Bus/Pci/PciBusDxe/PciIo.c
@@ -1305,11 +1305,11 @@ ModifyRootBridgeAttributes (
   }
 
   //
-  // Mask off EFI_PCI_IO_ATTRIBUTE_EMBEDDED_DEVICE & 
-  // EFI_PCI_IO_ATTRIBUTE_EMBEDDED_ROM, which are not supported by PCI root bridge.
+  // Mask off attributes not supported by PCI root bridge.
   //
   Attributes &= ~(UINT64)(EFI_PCI_IO_ATTRIBUTE_EMBEDDED_DEVICE |
-                          EFI_PCI_IO_ATTRIBUTE_EMBEDDED_ROM);
+                          EFI_PCI_IO_ATTRIBUTE_EMBEDDED_ROM |
+                          EFI_PCI_IO_ATTRIBUTE_DUAL_ADDRESS_CYCLE);
 
   //
   // Record the new attribute of the Root Bridge