@@ -285,11 +285,13 @@
 	if (_writtenLength != _length && exception == nil)
 		return true;
 
 # ifdef OF_HAVE_BLOCKS
 	if (_block != NULL) {
-		if (!_block(object, _buffer, _writtenLength, exception))
+		_length = _block(object, &_buffer, _writtenLength, exception);
+
+		if (_length == 0)
 			return false;
 
 		_writtenLength = 0;
 		return true;
 	} else {
@@ -296,12 +298,14 @@
 # endif
 		bool (*func)(id, SEL, OFStream *, const void *, size_t, id,
 		    id) = (bool (*)(id, SEL, OFStream *, const void *, size_t,
 		    id, id))[_target methodForSelector: _selector];
 
-		if (!func(_target, _selector, object, _buffer, _writtenLength,
-		    _context, exception))
+		_length = func(_target, _selector, object, &_buffer,
+		    _writtenLength, _context, exception);
+
+		if (_length == 0)
 			return false;
 
 		_writtenLength = 0;
 		return true;
 # ifdef OF_HAVE_BLOCKS