diff --git a/requirements.txt b/requirements.txt
index 062cc69..60afdd7 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,7 +1,7 @@
-jupyter-book
-sphinx-last-updated-by-git
+jupyter-book==0.15.1
+sphinx-last-updated-by-git==0.3.6
 # TODO: remove after https://github.com/executablebooks/jupyter-book/pull/2048
 docutils!=0.18.*,!=0.19.*,!=0.20.0
-sphinx-subfigure
+sphinx-subfigure==0.2.4
 # TODO: remove after https://github.com/pydata/pydata-sphinx-theme/issues/1543
 pydata-sphinx-theme!=0.14.2