diff --git a/main/streams/plain_wrapper.c b/main/streams/plain_wrapper.c
index 36a055e8fb2..1b9e1c25012 100644
--- a/main/streams/plain_wrapper.c
+++ b/main/streams/plain_wrapper.c
@@ -765,7 +765,7 @@ static int php_stdiop_set_option(php_stream *stream, int option, int value, void
 					return fd == -1 ? PHP_STREAM_OPTION_RETURN_ERR : PHP_STREAM_OPTION_RETURN_OK;
 
 				case PHP_STREAM_TRUNCATE_SET_SIZE:
-					return ftruncate(fd, *(size_t*)ptrparam) == 0 ? PHP_STREAM_OPTION_RETURN_OK : PHP_STREAM_OPTION_RETURN_ERR;
+					return ftruncate(fd, *(ptrdiff_t*)ptrparam) == 0 ? PHP_STREAM_OPTION_RETURN_OK : PHP_STREAM_OPTION_RETURN_ERR;
 			}
 			
 		default: