diff --git a/MdePkg/Include/IndustryStandard/Acpi51.h b/MdePkg/Include/IndustryStandard/Acpi51.h
index 8ad40770a3..a39d65178c 100644
--- a/MdePkg/Include/IndustryStandard/Acpi51.h
+++ b/MdePkg/Include/IndustryStandard/Acpi51.h
@@ -1834,6 +1834,25 @@ typedef struct {
   UINT32    EntryCount;
 } EFI_ACPI_5_1_EINJ_TRIGGER_ACTION_TABLE;
 
+///
+/// Windows ACPI Emulated devices Table
+///
+typedef struct {
+  EFI_ACPI_DESCRIPTION_HEADER    Header;
+  ///
+  /// Container of a bitmask of Windows behavior that this system requires
+  /// Bit 0 - RTC good
+  /// Bit 1 - ACPI PM timer good
+  ///
+  UINT32                         EmulatedDeviceFlags;
+} EFI_ACPI_5_1_WAET_TABLE;
+
+///
+/// WAET Flags. All other bits are reserved and must be 0.
+///
+#define EFI_ACPI_5_1_WAET_FLAGS_RTC_GOOD            BIT0
+#define EFI_ACPI_5_1_WAET_FLAGS_ACPI_PM_TIMER_GOOD  BIT1
+
 ///
 /// Platform Communications Channel Table (PCCT)
 ///