diff --git a/include/windef.h b/include/windef.h
index 056f499a163..a39fd33caca 100644
--- a/include/windef.h
+++ b/include/windef.h
@@ -142,8 +142,12 @@ extern "C" {
 #define WINAPIV     __cdecl
 #define APIENTRY    WINAPI
 
+#ifndef _declspec
 #define _declspec(x)
+#endif
+#ifndef __declspec
 #define __declspec(x)
+#endif
 
 #define CONST       const