diff --git a/README.md b/README.md
index 91dfcb3..a00a283 100644
--- a/README.md
+++ b/README.md
@@ -1,5 +1,7 @@
 # My Scheme function collection
 
-Only for [Guile](https://www.gnu.org/software/guile/) just now,
+**WARNING: No stable API**
+
+Only for [Guile](https://www.gnu.org/software/guile/) just now.
 
 ## Documentation (TODO)