Index: src/OFThread.h
==================================================================
--- src/OFThread.h
+++ src/OFThread.h
@@ -66,11 +66,11 @@
 		OF_THREAD_RUNNING,
 		OF_THREAD_WAITING_FOR_JOIN
 	} _running;
 	void *_pool;
 # ifdef OF_HAVE_BLOCKS
-	of_thread_block_t _threadBlock;
+	of_thread_block_t _Nullable _threadBlock;
 # endif
 	id _returnValue;
 	OFRunLoop *_Nullable _runLoop;
 	OFMutableDictionary *_threadDictionary;
 @private
@@ -84,11 +84,12 @@
 
 # ifdef OF_HAVE_BLOCKS
 /*!
  * The block to execute in the thread.
  */
-@property (readonly, nonatomic) of_thread_block_t threadBlock;
+@property OF_NULLABLE_PROPERTY (readonly, nonatomic)
+    of_thread_block_t threadBlock;
 # endif
 
 /*!
  * @brief Creates a new thread.
  *