diff --git a/README.md b/README.md
index 5d38fe9cbe2bd5d48bbc01f4d125f51adf1fd846..3d3b95e6c42306ad2d14a245b2a421a1bf0df660 100644
--- a/README.md
+++ b/README.md
@@ -8,6 +8,7 @@ Remember to add the following keys to your site in order for the module to work:
 * POLARIS_API_STAFF_USERNAME
 * POLARIS_API_STAFF_PASSWORD
 * POLARIS_API_WORKSTATION_ID
+* POLARIS_API_DEFAULT_PATRON_BRANCH_ID
 
 TODO:
 - Polaris core client in src/RCPL should be added as a new project on packagist