diff --git a/README.md b/README.md
index cd2b29e..991fc46 100644
--- a/README.md
+++ b/README.md
@@ -10,6 +10,8 @@ for the available Ruby versions.
 The action works for the `ubuntu-16.04`, `ubuntu-18.04` and `macos-latest` GitHub-hosted runners.  
 `windows-latest` is not yet supported.
 
+The prebuilt rubies are generated by https://github.com/eregon/ruby-install-builder.
+
 ## Usage
 
 Single job: