@@ -66,19 +66,17 @@
 
 #ifdef __GNUC__
 # define OF_INLINE inline __attribute__((__always_inline__))
 # define OF_LIKELY(cond) (__builtin_expect(!!(cond), 1))
 # define OF_UNLIKELY(cond) (__builtin_expect(!!(cond), 0))
-# define OF_UNAVAILABLE __attribute__((__unavailable__))
 # define OF_CONST_FUNC __attribute__((__const__))
 # define OF_NO_RETURN_FUNC __attribute__((__noreturn__))
 # define OF_WEAK_REF(sym) __attribute__((__weakref__(sym)))
 #else
 # define OF_INLINE inline
 # define OF_LIKELY(cond) cond
 # define OF_UNLIKELY(cond) cond
-# define OF_UNAVAILABLE
 # define OF_CONST_FUNC
 # define OF_NO_RETURN_FUNC
 # define OF_WEAK_REF(sym)
 #endif
 
@@ -200,10 +198,16 @@
 # define OF_NO_RETURN __attribute__((__noreturn__))
 #else
 # define OF_SENTINEL
 # define OF_NO_RETURN
 #endif
+
+#if __has_attribute(__unavailable__)
+# define OF_UNAVAILABLE __attribute__((__unavailable__))
+#else
+# define OF_UNAVAILABLE
+#endif
 
 #if __has_attribute(__objc_requires_super__)
 # define OF_REQUIRES_SUPER __attribute__((__objc_requires_super__))
 #else
 # define OF_REQUIRES_SUPER