diff --git a/README.md b/README.md
index 8e9038b1e9de01c3f0f3af684d86c8f03a485756..c746edbeaeae4f78199c7c8f795ce4bc21958b1c 100644
--- a/README.md
+++ b/README.md
@@ -70,6 +70,9 @@ To set up an `opam` switch that allows testing Sek, type this (only once):
 ```
   make -C fuzz setup
 ```
+The switch that is used for testing is defined in `fuzz/Makefile`;
+by default, at the time of writing, it is `4.11.1+afl`.
+
 You must also install [AFL](https://github.com/google/AFL).
 
 Then, to test the library using `afl-fuzz`, type: