@@ -114,12 +114,12 @@
  *
  * @param parser The parser which found an unknown entity
  * @param entity The name of the entity the XML parser didn't know
  * @return A substitution for the entity or `nil`
  */
--      (OFString *)parser: (OFXMLParser *)parser
-  foundUnknownEntityNamed: (OFString *)entity;
+- (nullable OFString *)parser: (OFXMLParser *)parser
+      foundUnknownEntityNamed: (OFString *)entity;
 @end
 
 /*!
  * @class OFXMLParser OFXMLParser.h ObjFW/OFXMLParser.h
  *