diff --git a/MdePkg/Include/Library/BaseLib.h b/MdePkg/Include/Library/BaseLib.h
index 24f93c9bb1..01d7f0eea9 100644
--- a/MdePkg/Include/Library/BaseLib.h
+++ b/MdePkg/Include/Library/BaseLib.h
@@ -5079,17 +5079,39 @@ typedef struct {
 ///
 /// Byte packed structure for an Interrupt Gate Descriptor
 ///
+#if defined (MDE_CPU_IA32)
+
 typedef union {
   struct {
-    UINT32  OffsetLow:16;   /// Offset bits 15..0
-    UINT32  Selector:16;    /// Selector
-    UINT32  Reserved_0:8;   /// Reserved
-    UINT32  GateType:8;     /// Gate Type.  See #defines above
-    UINT32  OffsetHigh:16;  /// Offset bits 31..16
+    UINT32  OffsetLow:16;   // Offset bits 15..0
+    UINT32  Selector:16;    // Selector
+    UINT32  Reserved_0:8;   // Reserved
+    UINT32  GateType:8;     // Gate Type.  See #defines above
+    UINT32  OffsetHigh:16;  // Offset bits 31..16
   } Bits;
   UINT64  Uint64;
 } IA32_IDT_GATE_DESCRIPTOR;
 
+#endif
+
+#if defined (MDE_CPU_X64)
+
+typedef union {
+  struct {
+    UINT32  OffsetLow:16;   // Offset bits 15..0
+    UINT32  Selector:16;    // Selector
+    UINT32  Reserved_0:8;   // Reserved
+    UINT32  GateType:8;     // Gate Type.  See #defines above
+    UINT32  OffsetHigh:16;  // Offset bits 31..16
+    UINT32  OffsetUpper:32; // Offset bits 63..32
+    UINT32  Reserved_1:32;  // Reserved
+  } Bits;
+  UINT64  Uint64;
+  UINT64  Uint64_1;
+} IA32_IDT_GATE_DESCRIPTOR;
+
+#endif
+
 ///
 /// Byte packed structure for an FP/SSE/SSE2 context
 ///