@@ -22,9 +22,10 @@
 /*!
  * @class OFSHA224Hash OFSHA224Hash.h ObjFW/OFSHA224Hash.h
  *
  * @brief A class which provides methods to create an SHA-224 hash.
  */
+OF_SUBCLASSING_RESTRICTED
 @interface OFSHA224Hash: OFSHA224Or256Hash
 @end
 
 OF_ASSUME_NONNULL_END