diff --git a/packages/xen-api/USAGE.md b/packages/xen-api/USAGE.md
index 19b446e9a..c73f6af90 100644
--- a/packages/xen-api/USAGE.md
+++ b/packages/xen-api/USAGE.md
@@ -34,6 +34,7 @@ Options:
 - `auth`: credentials used to sign in (can also be specified in the URL)
 - `readOnly = false`: if true, no methods with side-effects can be called
 - `callTimeout`: number of milliseconds after which a call is considered failed (can also be a map of timeouts by methods)
+- `httpProxy`: URL of the HTTP/HTTPS proxy used to reach the host, can include credentials
 
 ```js
 // Force connection.