diff --git a/requirements.txt b/requirements.txt
index 2b87f61..0f7025c 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -2,6 +2,7 @@
 pytest-cov
 setuptools
 sphinx
+sphinx-rtd-theme
 wheel
 
 # Runtime dependencies, must match install_requires in setup.py