diff --git a/README.md b/README.md
index 460137ae..8e96de7f 100644
--- a/README.md
+++ b/README.md
@@ -81,6 +81,7 @@ following programs installed for the test suite:
 * `sqlite3`
 * `rad` (from Radicle)
 * `git-remote-rad` (from Radicle)
+* `subplot` (Instructions [here](https://subplot.tech/download/). Required for `doc` make target.)
 
 ## Configuration