diff --git a/roles/prepare-workspace/README.rst b/roles/prepare-workspace/README.rst
index 10ea71857..9ca8d4267 100644
--- a/roles/prepare-workspace/README.rst
+++ b/roles/prepare-workspace/README.rst
@@ -5,3 +5,10 @@ This role is intended to run before any other role in a Zuul job.
 It starts the Zuul console streamer on every host in the inventory,
 and then copies the prepared source repos to the working directory on
 every host.
+
+**Role Variables**
+
+.. zuul:rolevar:: zuul_workspace_root
+   :default: .
+
+   The directory into which the source repositories are copied.