diff --git a/.github/workflows/build_docs.yml b/.github/workflows/build_docs.yml
index b516d98d..f7fd272b 100644
--- a/.github/workflows/build_docs.yml
+++ b/.github/workflows/build_docs.yml
@@ -119,7 +119,7 @@ jobs:
       - name: List book languages
         id: list-langs
         run: |
-          echo "matrix=$($HEXDOC --list-langs)" >> "$GITHUB_OUTPUT"
+          echo "matrix='$($HEXDOC --list-langs)'" >> "$GITHUB_OUTPUT"
           if [[ $RUNNER_DEBUG ]]; then
             tree -I '__pycache__|Common|Fabric|Forge|venv'
           fi