diff --git a/README.md b/README.md
index dc81124d..1fccaac1 100644
--- a/README.md
+++ b/README.md
@@ -3,7 +3,7 @@
 [![Build Status](https://travis-ci.org/picrin-scheme/picrin.png)](https://travis-ci.org/picrin-scheme/picrin)
 [![Docs Status](https://readthedocs.org/projects/picrin/badge/?version=latest)](https://picrin.readthedocs.org/)
 
-Picrin is a lightweight scheme implementation intended to comply with full R7RS specification. Its code is written in pure C99 and does not require any special external libraries installed on the platform.
+Picrin is a lightweight scheme implementation intended to comply with full R7RS specification. Its code is written in pure C89 and does not require any special external libraries installed on the platform.
 
 ## Documentation
 
diff --git a/docs/intro.rst b/docs/intro.rst
index 429bc045..5cc22c15 100644
--- a/docs/intro.rst
+++ b/docs/intro.rst
@@ -1,7 +1,7 @@
 Introduction
 ============
 
-Picrin is a lightweight scheme implementation intended to comply with full R7RS specification. Its code is written in pure C99 and does not require any special external libraries installed on the platform.
+Picrin is a lightweight scheme implementation intended to comply with full R7RS specification. Its code is written in pure C89 and does not require any special external libraries installed on the platform.
 
 - R7RS compatibility
 - reentrant design (all VM states are stored in single global state object)