@@ -14,10 +14,12 @@
  * file.
  */
 
 #import "OFString.h"
 
+OF_ASSUME_NONNULL_BEGIN
+
 /*! @file */
 
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -33,12 +35,12 @@
  *
  * @param string The XML string which contains an unknown entity
  * @param entity The XML entity which is unknown
  * @return A replacement string for the unknown entity
  */
-typedef OFString* (^of_string_xml_unescaping_block_t)(OFString *string,
-    OFString *entity);
+typedef __nullable OFString* (^of_string_xml_unescaping_block_t)(
+    OFString *string, OFString *entity);
 #endif
 
 /*!
  * @protocol OFStringXMLUnescapingDelegate OFString.h ObjFW/OFString.h
  *
@@ -73,11 +75,11 @@
  *	  unknown entities.
  *
  * @param delegate An OFXMLUnescapingDelegate as a handler for unknown entities
  */
 - (OFString*)stringByXMLUnescapingWithDelegate:
-    (id <OFStringXMLUnescapingDelegate>)delegate;
+    (nullable id <OFStringXMLUnescapingDelegate>)delegate;
 
 #ifdef OF_HAVE_BLOCKS
 /*!
  * @brief Unescapes XML in the string and uses the specified block for unknown
  *	  entities.
@@ -86,5 +88,7 @@
  */
 - (OFString*)stringByXMLUnescapingWithBlock:
     (of_string_xml_unescaping_block_t)block;
 #endif
 @end
+
+OF_ASSUME_NONNULL_END