diff --git a/MdePkg/Include/IndustryStandard/DebugPort2Table.h b/MdePkg/Include/IndustryStandard/DebugPort2Table.h
index 3faa30b76a..9ccfc1b1ee 100644
--- a/MdePkg/Include/IndustryStandard/DebugPort2Table.h
+++ b/MdePkg/Include/IndustryStandard/DebugPort2Table.h
@@ -47,6 +47,7 @@ typedef struct {
 #define   EFI_ACPI_DBG2_PORT_SUBTYPE_SERIAL_ARM_SBSA_GENERIC_UART                      0x000e
 #define   EFI_ACPI_DBG2_PORT_SUBTYPE_SERIAL_DCC                                        0x000f
 #define   EFI_ACPI_DBG2_PORT_SUBTYPE_SERIAL_BCM2835_UART                               0x0010
+#define   EFI_ACPI_DBG2_PORT_SUBTYPE_SERIAL_16550_WITH_GAS                             0x0012
 #define EFI_ACPI_DBG2_PORT_TYPE_1394                                                   0x8001
 #define   EFI_ACPI_DBG2_PORT_SUBTYPE_1394_STANDARD                                     0x0000
 #define EFI_ACPI_DBG2_PORT_TYPE_USB                                                    0x8002
diff --git a/MdePkg/Include/IndustryStandard/SerialPortConsoleRedirectionTable.h b/MdePkg/Include/IndustryStandard/SerialPortConsoleRedirectionTable.h
index 2066c7895e..7796796afe 100644
--- a/MdePkg/Include/IndustryStandard/SerialPortConsoleRedirectionTable.h
+++ b/MdePkg/Include/IndustryStandard/SerialPortConsoleRedirectionTable.h
@@ -100,6 +100,11 @@ typedef struct {
 ///
 #define EFI_ACPI_SERIAL_PORT_CONSOLE_REDIRECTION_TABLE_INTERFACE_TYPE_BCM2835_UART              0x10
 
+///
+/// 16550-compatible with parameters defined in Generic Address Structure
+///
+#define EFI_ACPI_SERIAL_PORT_CONSOLE_REDIRECTION_TABLE_INTERFACE_TYPE_16550_WITH_GAS            0x12
+
 //
 // Interrupt Type
 //