@@ -13,9 +13,13 @@
  * LICENSE.GPLv2 or LICENSE.GPLv3 respectively included in the packaging of this
  * file.
  */
 
 #import "OFTimer.h"
+
+OF_ASSUME_NONNULL_BEGIN
 
 @interface OFTimer (OF_PRIVATE_CATEGORY)
-- (void)OF_setInRunLoop: (OFRunLoop*)inRunLoop;
+- (void)OF_setInRunLoop: (nullable OFRunLoop*)inRunLoop;
 @end
+
+OF_ASSUME_NONNULL_END