Index: src/OFObject.h
==================================================================
--- src/OFObject.h
+++ src/OFObject.h
@@ -31,15 +31,17 @@
 # import <objfw-rt.h>
 #else
 # import <objc/objc.h>
 #endif
 
-#if defined(__has_feature) && __has_feature(objc_bool)
-# undef YES
-# define YES __objc_yes
-# undef NO
-# define NO __objc_no
+#ifdef __has_feature
+# if __has_feature(objc_bool)
+#  undef YES
+#  define YES __objc_yes
+#  undef NO
+#  define NO __objc_no
+# endif
 #endif
 
 #define OF_RETAIN_COUNT_MAX UINT_MAX
 #define OF_INVALID_INDEX SIZE_MAX