diff --git a/Source/LexerParser/cmListFileLexer.c b/Source/LexerParser/cmListFileLexer.c
index c726415be8661035235d0b330f24adc04896b9b9..15dcda04a01ead978a94456b73e34ecce4051612 100644
--- a/Source/LexerParser/cmListFileLexer.c
+++ b/Source/LexerParser/cmListFileLexer.c
@@ -766,7 +766,7 @@ Modify cmListFileLexer.c:
 
 /* IWYU pragma: no_forward_declare yyguts_t */
 
-#ifdef WIN32
+#ifdef _WIN32
 #include "cmsys/Encoding.h"
 #endif
 
diff --git a/Source/LexerParser/cmListFileLexer.in.l b/Source/LexerParser/cmListFileLexer.in.l
index 6a6fb5f06f173cd44874dc3e5cc9f84f637c017b..fdf14d2d38e6fc336a481d553c7bd87ab960529c 100644
--- a/Source/LexerParser/cmListFileLexer.in.l
+++ b/Source/LexerParser/cmListFileLexer.in.l
@@ -18,7 +18,7 @@ Modify cmListFileLexer.c:
 
 /* IWYU pragma: no_forward_declare yyguts_t */
 
-#ifdef WIN32
+#ifdef _WIN32
 #include "cmsys/Encoding.h"
 #endif