@@ -15,10 +15,12 @@
  */
 
 #import "OFObject.h"
 #import "OFConstantString.h"
 
+OF_ASSUME_NONNULL_BEGIN
+
 /*!
  * @class OFOptionsParser OFOptionsParser.h ObjFW/OFOptionsParser.h
  *
  * @brief A class for parsing the program options specified on the command line.
  */
@@ -80,14 +82,16 @@
  * @brief Returns the argument for the last parsed option, or nil if the last
  *	  parsed option takes no argument.
  *
  * @return The argument for the last parsed option
  */
-- (OFString*)argument;
+- (nullable OFString*)argument;
 
 /*!
  * @brief Returns the arguments following the last option.
  *
  * @return The arguments following the last option
  */
 - (OFArray OF_GENERIC(OFString*)*)remainingArguments;
 @end
+
+OF_ASSUME_NONNULL_END