diff --git a/doc/requirements.txt b/doc/requirements.txt
index 658e11b413ef5544b5a673e4ad798ca9b4be2c39..9de2b5124a4efac9bac919d0b6b652641e20f0d7 100644
--- a/doc/requirements.txt
+++ b/doc/requirements.txt
@@ -5,3 +5,4 @@
 # See .readthedocs.yaml in the root of this repository.
 breathe
 myst-parser
+sphinx_rtd_theme