diff --git a/docs/conf.py b/docs/conf.py
index 458bc6087..c3418cfb3 100644
--- a/docs/conf.py
+++ b/docs/conf.py
@@ -286,6 +286,7 @@ intersphinx_mapping = {
     'sphinx': ('https://www.sphinx-doc.org/en/master', None),
     'tox': ('https://tox.readthedocs.io/en/latest', None),
     'twisted': ('https://twistedmatrix.com/documents/current', None),
+    'twistedapi': ('https://twistedmatrix.com/documents/current/api', None),
 }