@@ -14,10 +14,12 @@
  * file.
  */
 
 #import "OFString.h"
 
+OF_ASSUME_NONNULL_BEGIN
+
 /*!
  * @class OFMutableString OFString.h ObjFW/OFString.h
  *
  * @brief A class for storing and modifying strings.
  */
@@ -205,5 +207,7 @@
 /*!
  * @brief Converts the mutable string to an immutable string.
  */
 - (void)makeImmutable;
 @end
+
+OF_ASSUME_NONNULL_END