diff --git a/panda/src/display/customGraphicsWindowProc.cxx b/panda/src/display/customGraphicsWindowProc.cxx
index cab48df3d1..6450d27fff 100644
--- a/panda/src/display/customGraphicsWindowProc.cxx
+++ b/panda/src/display/customGraphicsWindowProc.cxx
@@ -26,7 +26,7 @@ CustomGraphicsWindowProc::~CustomGraphicsWindowProc(){
   Py_DECREF(_handler);
 }
 
-#if defined(__WIN32__) || defined(_WIN32)
+#ifdef WIN32
 LONG CustomGraphicsWindowProc::wnd_proc(HWND hwnd, UINT msg, WPARAM wparam, LPARAM lparam){
   PyObject* ret = PyObject_CallFunction(_handler, "IIII", hwnd, msg, wparam, lparam);
   Py_XDECREF(ret);
diff --git a/panda/src/display/customGraphicsWindowProc.h b/panda/src/display/customGraphicsWindowProc.h
index bc64221fb2..28bcdad9d4 100644
--- a/panda/src/display/customGraphicsWindowProc.h
+++ b/panda/src/display/customGraphicsWindowProc.h
@@ -23,7 +23,7 @@ public:
   CustomGraphicsWindowProc(PyObject* handler, PyObject* name);
   virtual ~CustomGraphicsWindowProc();
 
-#if defined(__WIN32__) || defined(_WIN32)
+#ifdef WIN32
   virtual LONG wnd_proc(HWND hwnd, UINT msg, WPARAM wparam, LPARAM lparam);
 #endif
 
diff --git a/panda/src/display/graphicsWindowProc.h b/panda/src/display/graphicsWindowProc.h
index 6093526b71..8034131544 100644
--- a/panda/src/display/graphicsWindowProc.h
+++ b/panda/src/display/graphicsWindowProc.h
@@ -19,11 +19,11 @@
 #include "pandabase.h"
 #include "typedReferenceCount.h"
 
-#if defined(__WIN32__) || defined(_WIN32)
-	#ifndef WIN32_LEAN_AND_MEAN
-		#define WIN32_LEAN_AND_MEAN 1
-	#endif
-	#include <windows.h>
+#ifdef WIN32
+#ifndef WIN32_LEAN_AND_MEAN
+#define WIN32_LEAN_AND_MEAN 1
+#endif
+#include <windows.h>
 #endif
 
 /*
@@ -60,4 +60,4 @@ private:
   static TypeHandle _type_handle;
 };
 
-#endif //GRAPHICSWINDOWPROC_H
\ No newline at end of file
+#endif //GRAPHICSWINDOWPROC_H