diff --git a/.github/workflows/build-book.yaml b/.github/workflows/build-book.yaml
index 76b81c6..bff7f66 100644
--- a/.github/workflows/build-book.yaml
+++ b/.github/workflows/build-book.yaml
@@ -53,6 +53,8 @@ jobs:
         shell: bash -l {0}
     steps:
       - uses: actions/checkout@v3
+      - name: Install sphinx
+        run: pip install sphinx==5.3
       - name: Build the book
         run: |
           # copy baltrad notebooks to book dir