diff --git a/requirements.txt b/requirements.txt
index 32e08f2..5ac0b37 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -4,7 +4,7 @@ nbsphinx==0.3.2
 pre-commit
 pytest
 pytest-cov
-sphinx
+sphinx<1.6
 sphinx-prompt
 tox