diff --git a/src/gfx2.rc b/src/gfx2.rc
index e1976ed3..42975207 100644
--- a/src/gfx2.rc
+++ b/src/gfx2.rc
@@ -8,7 +8,7 @@
 FILEVERSION     2,6,0,2100
 PRODUCTVERSION  2,6,0,2100
 FILEFLAGSMASK   VS_FF_DEBUG
-#ifdef DEBUG
+#ifdef _DEBUG
 FILEFLAGS       VS_FF_DEBUG
 #else
 FILEFLAGS       0
diff --git a/src/gfx2log.c b/src/gfx2log.c
index a95221d6..f5be9857 100644
--- a/src/gfx2log.c
+++ b/src/gfx2log.c
@@ -19,6 +19,9 @@
     along with Grafx2; if not, see <http://www.gnu.org/licenses/>
 */
 
+#if defined(_MSC_VER)
+#include <windows.h>
+#endif
 #if defined(USE_SDL2)
 #include <SDL.h>
 #endif
@@ -34,7 +37,7 @@ extern void GFX2_Log(GFX2_Log_priority_T priority, const char * fmt, ...)
   va_start(ap, fmt);
   GFX2_LogV(priority, fmt, ap);
   va_end(ap);
-#if defined(_MSC_VER) && defined(DEBUG)
+#if defined(_MSC_VER) && defined(_DEBUG)
   {
     char message[1024];
     va_start(ap, fmt);
@@ -47,7 +50,7 @@ extern void GFX2_Log(GFX2_Log_priority_T priority, const char * fmt, ...)
 
 extern void GFX2_LogV(GFX2_Log_priority_T priority, const char * fmt, va_list ap)
 {
-#if !defined(DEBUG)
+#if !defined(_DEBUG)
   if ((unsigned)GFX2_verbosity_level < (unsigned)priority)
     return;
 #endif
diff --git a/src/main.c b/src/main.c
index b102cbca..e72844c3 100644
--- a/src/main.c
+++ b/src/main.c
@@ -211,7 +211,7 @@ void Error_function(int error_code, const char *filename, int line_number, const
 
   snprintf(msg_buffer, sizeof(msg_buffer), "Error number %d occured in file %s, line %d, function %s.\n", error_code, filename,line_number,function_name);
   fputs(msg_buffer, stderr);
-#if defined(_MSC_VER) && defined(DEBUG)
+#if defined(_MSC_VER) && defined(_DEBUG)
   OutputDebugStringA(msg_buffer);
 #endif
 
@@ -277,7 +277,7 @@ void Error_function(int error_code, const char *filename, int line_number, const
     {
       fputs(msg, stderr);
 #if defined(WIN32)
-#if defined(DEBUG)
+#if defined(_DEBUG)
       OutputDebugStringA(msg);
 #endif
       MessageBoxA(GFX2_Get_Window_Handle(), msg, "GrafX2 error", MB_OK | MB_ICONERROR);