Index: src/OFObject.h
==================================================================
--- src/OFObject.h
+++ src/OFObject.h
@@ -30,10 +30,17 @@
 #ifdef OF_OBJFW_RUNTIME
 # 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
+#endif
 
 #define OF_RETAIN_COUNT_MAX UINT_MAX
 #define OF_INVALID_INDEX SIZE_MAX
 
 /**