@@ -23,10 +23,11 @@
 /*!
  * @class OFHMAC OFHMAC.h ObjFW/OFHMAC.h
  *
  * @brief A class which provides methods to calculate an HMAC.
  */
+OF_SUBCLASSING_RESTRICTED
 @interface OFHMAC: OFObject
 {
 	Class <OFCryptoHash> _hashClass;
 	id <OFCryptoHash> _Nullable _outerHash, _innerHash;
 	id <OFCryptoHash> _Nullable _outerHashCopy, _innerHashCopy;