@@ -44,16 +44,22 @@
 #endif
 
 #ifndef __has_feature
 # define __has_feature(x) 0
 #endif
+
+#ifdef __GNUC__
+# define __GCC_VERSION__ (__GNUC__ * 100 + __GNUC_MINOR__)
+#else
+# define __GCC_VERSION__ 0
+#endif
 
 #if defined(__clang__)
 # define OF_HAVE_PROPERTIES
 # define OF_HAVE_OPTIONAL_PROTOCOLS
 # define OF_HAVE_FAST_ENUMERATION
-#elif defined(__GNUC__) && (__GNUC__ * 100 + __GNUC__) >= 406
+#elif __GCC_VERSION__ >= 406
 # define OF_HAVE_PROPERTIES
 # define OF_HAVE_OPTIONAL_PROTOCOLS
 # define OF_HAVE_FAST_ENUMERATION
 #endif
 
@@ -69,10 +75,14 @@
 # undef YES
 # define YES __objc_yes
 # undef NO
 # define NO __objc_no
 #endif
+
+#if defined(__clang__) || __GCC_VERSION__ >= 406
+# define OF_SENTINEL __attribute__((sentinel))
+#endif
 
 #if __has_feature(objc_arc)
 # define OF_RETURNS_RETAINED __attribute__((ns_returns_retained))
 # define OF_RETURNS_NOT_RETAINED __attribute__((ns_returns_not_retained))
 # define OF_RETURNS_INNER_POINTER __attribute__((objc_returns_inner_pointer))