diff --git a/Modules/ThirdParty/GDCM/src/gdcm/Utilities/gdcmopenjpeg-v2/libopenjpeg/opj_malloc.h b/Modules/ThirdParty/GDCM/src/gdcm/Utilities/gdcmopenjpeg-v2/libopenjpeg/opj_malloc.h
index ebb3c85dfc7..624459ba3b3 100644
--- a/Modules/ThirdParty/GDCM/src/gdcm/Utilities/gdcmopenjpeg-v2/libopenjpeg/opj_malloc.h
+++ b/Modules/ThirdParty/GDCM/src/gdcm/Utilities/gdcmopenjpeg-v2/libopenjpeg/opj_malloc.h
@@ -64,7 +64,7 @@ Allocate memory aligned to a 16 byte boundry
 @return Returns a void pointer to the allocated space, or NULL if there is insufficient memory available
 */
 /* FIXME: These should be set with cmake tests, but we're currently not requiring use of cmake */
-#ifdef WIN32
+#ifdef _WIN32
   /* Someone should tell the mingw people that their malloc.h ought to provide _mm_malloc() */
   #ifdef __GNUC__
     #include <mm_malloc.h>