diff --git a/requirements.txt b/requirements.txt
index 2fb7c5d..8a5e4a2 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -2,6 +2,7 @@ bumpversion
 ipython
 nbsphinx==0.4.3
 pre-commit
+pygments<3,>=2.4.1
 pytest
 pytest-cov
 sphinx<2