diff --git a/README.md b/README.md
index b5c8231..0d1960d 100644
--- a/README.md
+++ b/README.md
@@ -14,6 +14,7 @@ python3 -m thursday
 ## prerequisites
 
 * Python 3.10 or greater
+* numpy 1.23
 * *TODO*
 
 ## structure