@@ -17,13 +17,14 @@
 
 #import "OFCharacterSet.h"
 
 OF_ASSUME_NONNULL_BEGIN
 
+OF_SUBCLASSING_RESTRICTED
 @interface OFBitSetCharacterSet: OFCharacterSet
 {
 	unsigned char *_bitset;
 	size_t _size;
 }
 @end
 
 OF_ASSUME_NONNULL_END