diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index d48dae30e..3db8d687d 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -90,6 +90,13 @@ pre-commit run --all-files
 ```
 
 These checks will also run automatically before every commit.
+The command may fail with
+
+```
+RuntimeError: failed to find interpreter for Builtin discover of python_spec='python3.8'
+```
+
+You'll need to install python3.8 and make sure it's available in your PATH.
 
 ### Formatting