diff --git a/doc/lua_api.md b/doc/lua_api.md
index 877f9e71f..4ed1e5525 100644
--- a/doc/lua_api.md
+++ b/doc/lua_api.md
@@ -7999,6 +7999,7 @@ An `AsyncJob` is a reference to a job to be run in an async environment.
 ### Methods
 * `cancel()`: try to cancel the job
     * Returns whether the job was cancelled.
+    * A job can only be cancelled if it has not started.
 
 `InvRef`
 --------