diff --git a/docs/requirements.txt b/docs/requirements.txt
index b6742bcc..0b57f883 100644
--- a/docs/requirements.txt
+++ b/docs/requirements.txt
@@ -1,11 +1,13 @@
+appdirs
 attrs
-six
+matplotlib
+mpmath
 numba
-tskit
+pandas
 scipy
+six
+tskit
 tqdm
-appdirs
-pandas
 jupyter-book==0.15.1
 sphinx-issues==3.0.1
 sphinx-argparse==0.4.0