diff --git a/CMakeLists.txt b/CMakeLists.txt
index d93a36e1..0f39a509 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -2,7 +2,7 @@ cmake_minimum_required(VERSION 3.10)
 
 project(pocketpy)
 
-set(CMAKE_C_STANDARD 11)
+set(CMAKE_C_STANDARD 99)
 set(CMAKE_C_STANDARD_REQUIRED ON)
 
 # use IPO