@@ -22,11 +22,11 @@
 /*!
  * @class OFValue OFValue.h ObjFW/OFValue.h
  *
  * @brief A class for storing arbitrary values in an object.
  */
-@interface OFValue: OFObject
+@interface OFValue: OFObject <OFCopying>
 /*!
  * @brief The ObjC type encoding of the value.
  */
 @property (readonly, nonatomic) const char *objCType;