diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index f5252c3..b47b429 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -7,13 +7,13 @@ jobs:
     steps:
     - uses: actions/checkout@v1
     # PDF
-    - uses: ammaraskar/sphinx-action@master
+    - uses: ax3l/sphinx-action@newer-sphinx
       with:
         docs-folder: "docs/"
         pre-build-command: "apt-get update -y && apt-get install -y $(cat docs/ubuntu-package.list) && python -m pip install -r docs/requirements.txt"
         build-command: "make latexpdf"
     # HTML
-    - uses: ammaraskar/sphinx-action@master
+    - uses: ax3l/sphinx-action@newer-sphinx
       with:
         docs-folder: "docs/"
 
diff --git a/docs/requirements.txt b/docs/requirements.txt
index b61af89..a167126 100644
--- a/docs/requirements.txt
+++ b/docs/requirements.txt
@@ -1,6 +1,9 @@
 sphinx_rtd_theme>=0.3.1
 recommonmark
-sphinx
+sphinx>=2.0
+# docutils 0.17 breaks HTML tags & RTD theme
+# https://github.com/sphinx-doc/sphinx/issues/9001
+docutils<=0.16
 pygments
 # generate plots
 matplotlib