diff --git a/core/fpdfapi/font/cpdf_cidfont.cpp b/core/fpdfapi/font/cpdf_cidfont.cpp
index 91c5301..9ebda33 100644
--- a/core/fpdfapi/font/cpdf_cidfont.cpp
+++ b/core/fpdfapi/font/cpdf_cidfont.cpp
@@ -131,7 +131,7 @@
   return CPDF_ModuleMgr::Get()->GetPageModule()->GetFontGlobals();
 }
 
-#if _FX_PLATFORM_ != _FX_PLATFORM_WINDOWS_
+#if !defined(OS_WIN)
 
 bool IsValidEmbeddedCharcodeFromUnicodeCharset(CIDSet charset) {
   switch (charset) {
@@ -179,7 +179,7 @@
   return 0;
 }
 
-#endif  // _FX_PLATFORM_ != _FX_PLATFORM_WINDOWS_
+#endif  // !defined(OS_WIN)
 
 void FT_UseCIDCharmap(FXFT_Face face, int coding) {
   int encoding;
diff --git a/core/fxcrt/cfx_fileaccess_windows.h b/core/fxcrt/cfx_fileaccess_windows.h
index a430b53..a95466f 100644
--- a/core/fxcrt/cfx_fileaccess_windows.h
+++ b/core/fxcrt/cfx_fileaccess_windows.h
@@ -7,10 +7,11 @@
 #ifndef CORE_FXCRT_CFX_FILEACCESS_WINDOWS_H_
 #define CORE_FXCRT_CFX_FILEACCESS_WINDOWS_H_
 
+#include "build/build_config.h"
 #include "core/fxcrt/fileaccess_iface.h"
 #include "core/fxcrt/fx_system.h"
 
-#if _FX_PLATFORM_ != _FX_PLATFORM_WINDOWS_
+#if !defined(OS_WIN)
 #error "Included on the wrong platform"
 #endif
 
diff --git a/core/fxcrt/fx_system_unittest.cpp b/core/fxcrt/fx_system_unittest.cpp
index 73f9c75..d32c8e2 100644
--- a/core/fxcrt/fx_system_unittest.cpp
+++ b/core/fxcrt/fx_system_unittest.cpp
@@ -4,6 +4,7 @@
 
 #include <limits>
 
+#include "build/build_config.h"
 #include "core/fxcrt/fx_string.h"
 #include "core/fxcrt/fx_system.h"
 #include "testing/gtest/include/gtest/gtest.h"
@@ -11,7 +12,7 @@
 // Unit test covering cases where PDFium replaces well-known library
 // functionality on any given platformn.
 
-#if _FX_PLATFORM_ != _FX_PLATFORM_WINDOWS_
+#if !defined(OS_WIN)
 
 namespace {
 
@@ -158,7 +159,7 @@
       "111111111111111111111111111111111111111111111111111111111111111");
 }
 
-#endif  // _FX_PLATFORM_ != _FX_PLATFORM_WINDOWS_
+#endif  // !defined(OS_WIN)
 
 TEST(fxcrt, FXSYS_wcsftime) {
   struct tm good_time = {};
diff --git a/core/fxge/cfx_font.cpp b/core/fxge/cfx_font.cpp
index 6234b15..0477747 100644
--- a/core/fxge/cfx_font.cpp
+++ b/core/fxge/cfx_font.cpp
@@ -320,7 +320,7 @@
   return true;
 }
 
-#if _FX_PLATFORM_ != _FX_PLATFORM_WINDOWS_
+#if !defined(OS_WIN)
 void CFX_Font::SetFace(FXFT_Face face) {
   ClearFaceCache();
   m_Face = face;
@@ -329,7 +329,7 @@
 void CFX_Font::SetSubstFont(std::unique_ptr<CFX_SubstFont> subst) {
   m_pSubstFont = std::move(subst);
 }
-#endif  // _FX_PLATFORM_ != _FX_PLATFORM_WINDOWS_
+#endif  // !defined(OS_WIN)
 #endif  // PDF_ENABLE_XFA
 
 CFX_Font::~CFX_Font() {
diff --git a/core/fxge/cfx_font.h b/core/fxge/cfx_font.h
index bc9cc85..e708f9b 100644
--- a/core/fxge/cfx_font.h
+++ b/core/fxge/cfx_font.h
@@ -55,10 +55,10 @@
 #ifdef PDF_ENABLE_XFA
   bool LoadFile(const RetainPtr<IFX_SeekableReadStream>& pFile, int nFaceIndex);
 
-#if _FX_PLATFORM_ != _FX_PLATFORM_WINDOWS_
+#if !defined(OS_WIN)
   void SetFace(FXFT_Face face);
   void SetSubstFont(std::unique_ptr<CFX_SubstFont> subst);
-#endif  // _FX_PLATFORM_ != _FX_PLATFORM_WINDOWS_
+#endif  // !defined(OS_WIN)
 #endif  // PDF_ENABLE_XFA
 
   const CFX_GlyphBitmap* LoadGlyphBitmap(uint32_t glyph_index,
diff --git a/xfa/fde/cfde_textout.cpp b/xfa/fde/cfde_textout.cpp
index 517b541..3015fe8 100644
--- a/xfa/fde/cfde_textout.cpp
+++ b/xfa/fde/cfde_textout.cpp
@@ -9,6 +9,7 @@
 #include <algorithm>
 #include <utility>
 
+#include "build/build_config.h"
 #include "core/fxcrt/fx_coordinates.h"
 #include "core/fxcrt/fx_system.h"
 #include "core/fxge/cfx_font.h"
@@ -53,7 +54,7 @@
     }
   }
 
-#if _FX_PLATFORM_ != _FX_PLATFORM_WINDOWS_
+#if !defined(OS_WIN)
   uint32_t dwFontStyle = pFont->GetFontStyles();
   CFX_Font FxFont;
   auto SubstFxFont = pdfium::MakeUnique<CFX_SubstFont>();
@@ -62,7 +63,7 @@
   SubstFxFont->m_WeightCJK = SubstFxFont->m_Weight;
   SubstFxFont->m_bItalicCJK = FontStyleIsItalic(dwFontStyle);
   FxFont.SetSubstFont(std::move(SubstFxFont));
-#endif  // _FX_PLATFORM_ != _FX_PLATFORM_WINDOWS_
+#endif
 
   RetainPtr<CFGAS_GEFont> pCurFont;
   TextCharPos* pCurCP = nullptr;
@@ -77,12 +78,12 @@
         pFxFont = pCurFont->GetDevFont();
 
         CFX_Font* font;
-#if _FX_PLATFORM_ != _FX_PLATFORM_WINDOWS_
+#if !defined(OS_WIN)
         FxFont.SetFace(pFxFont->GetFace());
         font = &FxFont;
 #else
         font = pFxFont;
-#endif  // _FX_PLATFORM_ != _FX_PLATFORM_WINDOWS_
+#endif
 
         device->DrawNormalText(iCurCount, pCurCP, font, -fFontSize, pMatrix,
                                color, FXTEXT_CLEARTYPE);
@@ -99,20 +100,20 @@
   if (pCurFont && iCurCount) {
     pFxFont = pCurFont->GetDevFont();
     CFX_Font* font;
-#if _FX_PLATFORM_ != _FX_PLATFORM_WINDOWS_
+#if !defined(OS_WIN)
     FxFont.SetFace(pFxFont->GetFace());
     font = &FxFont;
 #else
     font = pFxFont;
-#endif  // _FX_PLATFORM_ != _FX_PLATFORM_WINDOWS_
+#endif
 
     bRet = device->DrawNormalText(iCurCount, pCurCP, font, -fFontSize, pMatrix,
                                   color, FXTEXT_CLEARTYPE);
   }
 
-#if _FX_PLATFORM_ != _FX_PLATFORM_WINDOWS_
+#if !defined(OS_WIN)
   FxFont.SetFace(nullptr);
-#endif  // _FX_PLATFORM_ != _FX_PLATFORM_WINDOWS_
+#endif
 
   return bRet;
 }
diff --git a/xfa/fgas/font/cfgas_fontmgr.cpp b/xfa/fgas/font/cfgas_fontmgr.cpp
index c950999..b223765 100644
--- a/xfa/fgas/font/cfgas_fontmgr.cpp
+++ b/xfa/fgas/font/cfgas_fontmgr.cpp
@@ -24,7 +24,7 @@
 #include "xfa/fgas/font/cfgas_gefont.h"
 #include "xfa/fgas/font/fgas_fontutils.h"
 
-#if _FX_PLATFORM_ != _FX_PLATFORM_WINDOWS_
+#if !defined(OS_WIN)
 #include "xfa/fgas/font/cfx_fontsourceenum_file.h"
 #endif
 
@@ -911,9 +911,9 @@
   if (!pEFont)
     return;
 
-#if _FX_PLATFORM_ != _FX_PLATFORM_WINDOWS_
+#if !defined(OS_WIN)
   m_IFXFont2FileRead.erase(pEFont);
-#endif  // _FX_PLATFORM_ != _FX_PLATFORM_WINDOWS_
+#endif
 
   auto iter = m_Hash2Fonts.begin();
   while (iter != m_Hash2Fonts.end()) {
diff --git a/xfa/fgas/font/cfgas_gefont.cpp b/xfa/fgas/font/cfgas_gefont.cpp
index e5b0ed3..f57871f 100644
--- a/xfa/fgas/font/cfgas_gefont.cpp
+++ b/xfa/fgas/font/cfgas_gefont.cpp
@@ -239,7 +239,7 @@
   WideString wsFamily = GetFamilyName();
   RetainPtr<CFGAS_GEFont> pFont =
       m_pFontMgr->GetFontByUnicode(wUnicode, GetFontStyles(), wsFamily.c_str());
-#if _FX_PLATFORM_ != _FX_PLATFORM_WINDOWS_
+#if !defined(OS_WIN)
   if (!pFont)
     pFont = m_pFontMgr->GetFontByUnicode(wUnicode, GetFontStyles(), nullptr);
 #endif