diff --git a/MdePkg/Include/Ia32/ProcessorBind.h b/MdePkg/Include/Ia32/ProcessorBind.h
index 5f29bb3e09..e6d1a7da90 100644
--- a/MdePkg/Include/Ia32/ProcessorBind.h
+++ b/MdePkg/Include/Ia32/ProcessorBind.h
@@ -23,11 +23,11 @@
 //
 // Make sure we are using the correct packing rules per EFI specification
 //
-#ifndef __GNUC__
+#if !defined(__GNUC__)
 #pragma pack()
 #endif
 
-#if __INTEL_COMPILER
+#if defined(__INTEL_COMPILER)
 //
 // Disable ICC's remark #869: "Parameter" was never referenced warning.
 // This is legal ANSI C code so we disable the remark that is turned on with -Wall
@@ -49,7 +49,7 @@
 #endif
 
 
-#if _MSC_EXTENSIONS
+#if defined(_MSC_EXTENSIONS)
 
 //
 // Disable warning that make it impossible to compile at /W4
@@ -95,7 +95,7 @@
   // No ANSI C 2000 stdint.h integer width declarations, so define equivalents
   //
  
-  #if _MSC_EXTENSIONS 
+  #if defined(_MSC_EXTENSIONS)
 
     //
     // use Microsoft C complier dependent integer width types 
@@ -295,13 +295,13 @@ typedef INT32   INTN;
 // use the correct C calling convention. All protocol member functions and
 // EFI intrinsics are required to modify their member functions with EFIAPI.
 //
-#if _MSC_EXTENSIONS
+#if defined(_MSC_EXTENSIONS)
   ///
   /// Microsoft* compiler specific method for EFIAPI calling convension
   /// 
   #define EFIAPI __cdecl  
 #else
-  #if __GNUC__
+  #if defined(__GNUC__)
     ///
     /// GCC specific method for EFIAPI calling convension
     /// 
@@ -314,7 +314,7 @@ typedef INT32   INTN;
 //  if the /OPT:REF linker option is used. We defined a macro as this is a 
 //  a non standard extension
 //
-#if _MSC_EXTENSIONS
+#if defined(_MSC_EXTENSIONS)
   ///
   /// Remove global variable from the linked image if there are no references to 
   /// it after all compiler and linker optimizations have been performed.
@@ -331,7 +331,7 @@ typedef INT32   INTN;
 //
 // For symbol name in GNU assembly code, an extra "_" is necessary
 //
-#if __GNUC__
+#if defined(__GNUC__)
   #if defined(linux)
     #define ASM_PFX(name) name
   #else
diff --git a/MdePkg/Include/Ipf/ProcessorBind.h b/MdePkg/Include/Ipf/ProcessorBind.h
index d92f16ca27..eb31c3f7bd 100644
--- a/MdePkg/Include/Ipf/ProcessorBind.h
+++ b/MdePkg/Include/Ipf/ProcessorBind.h
@@ -28,7 +28,7 @@
 #pragma pack()
 
 
-#if __INTEL_COMPILER
+#if defined(__INTEL_COMPILER)
 //
 // Disable ICC's remark #869: "Parameter" was never referenced warning.
 // This is legal ANSI C code so we disable the remark that is turned on with -Wall
@@ -50,7 +50,7 @@
 #endif
 
 
-#if _MSC_EXTENSIONS
+#if defined(_MSC_EXTENSIONS)
 //
 // Disable warning that make it impossible to compile at /W4
 // This only works for Microsoft* tools
@@ -101,12 +101,12 @@
 #endif
 
 
-#if (__STDC_VERSION__ < 199901L)
+#if defined(__STDC_VERSION__) && (__STDC_VERSION__ < 199901L)
   //
   // No ANSI C 2000 stdint.h integer width declarations, so define equivalents
   //
 
-  #if _MSC_EXTENSIONS
+  #if defined(_MSC_EXTENSIONS)
     //
     // use Microsoft C complier dependent integer width types
     //
@@ -158,7 +158,7 @@
     ///
     typedef char                INT8;
   #else
-    #ifdef _EFI_P64
+    #if defined(_EFI_P64)
       //
       // P64 - pointers being 64-bit and longs and ints are 32-bits.
       //
@@ -358,7 +358,7 @@ typedef INT64   INTN;
 // use the correct C calling convention. All protocol member functions and
 // EFI intrinsics are required to modify their member functions with EFIAPI.
 //
-#if _MSC_EXTENSIONS
+#if defined(_MSC_EXTENSIONS)
   ///
   /// Microsoft* compiler specific method for EFIAPI calling convension
   /// 
@@ -372,7 +372,7 @@ typedef INT64   INTN;
 //  if the /OPT:REF linker option is used. We defined a macro as this is a
 //  a non standard extension
 //
-#if _MSC_EXTENSIONS
+#if defined(_MSC_EXTENSIONS)
   ///
   /// Remove global variable from the linked image if there are no references to 
   /// it after all compiler and linker optimizations have been performed.
diff --git a/MdePkg/Include/X64/ProcessorBind.h b/MdePkg/Include/X64/ProcessorBind.h
index f1b0339a12..71f5277538 100644
--- a/MdePkg/Include/X64/ProcessorBind.h
+++ b/MdePkg/Include/X64/ProcessorBind.h
@@ -24,12 +24,12 @@
 //
 // Make sure we are using the correct packing rules per EFI specification
 //
-#ifndef __GNUC__
+#if !defined(__GNUC__)
 #pragma pack()
 #endif
 
 
-#if __INTEL_COMPILER
+#if defined(__INTEL_COMPILER)
 //
 // Disable ICC's remark #869: "Parameter" was never referenced warning.
 // This is legal ANSI C code so we disable the remark that is turned on with -Wall
@@ -51,7 +51,7 @@
 #endif
 
 
-#if _MSC_EXTENSIONS
+#if defined(_MSC_EXTENSIONS)
 
 //
 // Disable warning that make it impossible to compile at /W4
@@ -97,7 +97,7 @@
   // No ANSI C 2000 stdint.h integer width declarations, so define equivalents
   //
  
-  #if _MSC_EXTENSIONS 
+  #if defined(_MSC_EXTENSIONS)
     //
     // use Microsoft C complier dependent integer width types 
     //
@@ -149,7 +149,7 @@
     ///
     typedef char                INT8;
   #else
-    #ifdef _EFI_P64 
+    #if defined(_EFI_P64)
       //
       // P64 - pointers being 64-bit and longs and ints are 32-bits.
       //
@@ -348,12 +348,12 @@ typedef INT64   INTN;
 // use the correct C calling convention. All protocol member functions and
 // EFI intrinsics are required to modify their member functions with EFIAPI.
 //
-#if _MSC_EXTENSIONS 
+#if defined(_MSC_EXTENSIONS)
   ///
   /// Microsoft* compiler specific method for EFIAPI calling convension
   /// 
   #define EFIAPI __cdecl  
-#elif __GNUC__
+#elif defined(__GNUC__)
   ///
   /// Define the standard calling convention reguardless of optimization level.
   /// The GCC support assumes a GCC compiler that supports the EFI ABI. The EFI
@@ -376,7 +376,7 @@ typedef INT64   INTN;
 //  if the /OPT:REF linker option is used. We defined a macro as this is a 
 //  a non standard extension
 //
-#if _MSC_EXTENSIONS
+#if defined(_MSC_EXTENSIONS)
   ///
   /// Remove global variable from the linked image if there are no references to 
   /// it after all compiler and linker optimizations have been performed.
@@ -395,7 +395,7 @@ typedef INT64   INTN;
 //
 // For symbol name in GNU assembly code, an extra "_" is necessary
 //
-#if __GNUC__
+#if defined(__GNUC__)
   #if defined(linux)
     #define ASM_PFX(name) name
   #else