diff --git a/Makefile b/Makefile
index ccd6d27..bdf06c6 100644
--- a/Makefile
+++ b/Makefile
@@ -1,4 +1,5 @@
-REV := master
+# 'master' or hash
+REV := 8ba9981e5
 BASE := https://raw.githubusercontent.com/cnlohr/ch32v003fun/$(REV)
 CURL_FLAGS := -O -\# --fail --location --tlsv1.3 --proto =https --max-time 300