diff --git a/prompb/README.md b/prompb/README.md
index 7f2439166..8c19b17e9 100644
--- a/prompb/README.md
+++ b/prompb/README.md
@@ -4,6 +4,6 @@ re-compile them when building Prometheus.
 If however you have modified the defs and do need to re-compile, run
 `make proto` from the parent dir.
 
-In order for the script to run, you'll need `protoc` (version 3.5.1) in your
+In order for the script to run, you'll need `protoc` (version 3.12.3) in your
 PATH.