@@ -1,7 +1,7 @@
 /*
- * Copyright (c) 2008-2021 Jonathan Schleifer <js@nil.im>
+ * Copyright (c) 2008-2022 Jonathan Schleifer <js@nil.im>
  *
  * All rights reserved.
  *
  * This file is part of ObjFW. It may be distributed under the terms of the
  * Q Public License 1.0, which can be found in the file LICENSE.QPL included in
@@ -40,12 +40,12 @@
 @end
 
 #ifdef __cplusplus
 extern "C" {
 #endif
-extern void *_Block_copy(const void *);
-extern void _Block_release(const void *);
+extern void *_Nullable _Block_copy(const void *_Nullable);
+extern void _Block_release(const void *_Nullable);
 
 # if defined(OF_WINDOWS) && \
     (defined(OF_NO_SHARED) || defined(OF_COMPILING_OBJFW))
 /*
  * Clang has implicit declarations for these, but they are dllimport. When