diff --git a/docs/user/advanced.rst b/docs/user/advanced.rst
index 7582f6b8..51fc925f 100644
--- a/docs/user/advanced.rst
+++ b/docs/user/advanced.rst
@@ -236,6 +236,7 @@ or persistent::
   the c_rehash utility supplied with OpenSSL.
 
 This list of trusted CAs can also be specified through the ``REQUESTS_CA_BUNDLE`` environment variable.
+If ``REQUESTS_CA_BUNDLE`` is not set, ``CURL_CA_BUNDLE`` will be used as fallback.
 
 Requests can also ignore verifying the SSL certificate if you set ``verify`` to False::