diff --git a/requirements.txt b/requirements.txt
index 8a5e4a2..fa1773a 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,5 +1,6 @@
 bumpversion
 ipython
+nbconvert<6
 nbsphinx==0.4.3
 pre-commit
 pygments<3,>=2.4.1