diff --git a/documentation/usage/env.rst b/documentation/usage/env.rst
index 994117afe..201d17eb7 100644
--- a/documentation/usage/env.rst
+++ b/documentation/usage/env.rst
@@ -3,6 +3,7 @@ Environment variables
 
 Betty reads the following environment variables:
 
-- ``BETTY_CACHE_DIRECTORY``: The path to a directory for Betty to use as its application cache. Defaults to ``.betty`` in the current user's home directory.
-- ``BETTY_CONCURRENCY``: The concurrency factor expressed as an integer. Defaults to the number of CPU cores. Set to ``1``
-  to disable concurrency altogether. Example: ``BETTY_CONCURRENCY=4``.
+``BETTY_CACHE_DIRECTORY``
+    The path to a directory for Betty to use as its application cache.
+    Defaults to ``.betty`` in the current user's home directory.
+    This is primarily used for testing an externally running Betty application.