diff --git a/include/guiddef.h b/include/guiddef.h
index a25b3a71077..d09ea98e468 100644
--- a/include/guiddef.h
+++ b/include/guiddef.h
@@ -86,6 +86,14 @@ extern "C++" {
 
 #undef DEFINE_GUID
 
+#ifndef DECLSPEC_HIDDEN
+# if defined(__GNUC__) && !defined(__MINGW32__) && !defined(__CYGWIN__)
+#  define DECLSPEC_HIDDEN __attribute__((visibility ("hidden")))
+# else
+#  define DECLSPEC_HIDDEN
+# endif
+#endif
+
 #ifdef INITGUID
 #ifdef __cplusplus
 #define DEFINE_GUID(name, l, w1, w2, b1, b2, b3, b4, b5, b6, b7, b8) \
diff --git a/include/winnt.h b/include/winnt.h
index 87051289445..53d9af8bf96 100644
--- a/include/winnt.h
+++ b/include/winnt.h
@@ -177,12 +177,14 @@ extern "C" {
 # define DECLSPEC_EXPORT
 #endif
 
-#if defined(_MSC_VER) || defined(__MINGW32__) || defined(__CYGWIN__) || defined(__sun)
-# define DECLSPEC_HIDDEN
-#elif defined(__GNUC__) && ((__GNUC__ > 3) || ((__GNUC__ == 3) && (__GNUC_MINOR__ >= 3)))
-# define DECLSPEC_HIDDEN __attribute__((visibility ("hidden")))
-#else
-# define DECLSPEC_HIDDEN
+#ifndef DECLSPEC_HIDDEN
+# if defined(_MSC_VER) || defined(__MINGW32__) || defined(__CYGWIN__) || defined(__sun)
+#  define DECLSPEC_HIDDEN
+# elif defined(__GNUC__) && ((__GNUC__ > 3) || ((__GNUC__ == 3) && (__GNUC_MINOR__ >= 3)))
+#  define DECLSPEC_HIDDEN __attribute__((visibility ("hidden")))
+# else
+#  define DECLSPEC_HIDDEN
+# endif
 #endif
 
 #ifndef __has_attribute