diff --git a/.github/actions/install-sphinx-markdown-builder/action.yml b/.github/actions/install-sphinx-markdown-builder/action.yml
index 88f29fbce..1374d6f86 100644
--- a/.github/actions/install-sphinx-markdown-builder/action.yml
+++ b/.github/actions/install-sphinx-markdown-builder/action.yml
@@ -6,7 +6,9 @@ permissions:
 runs:
   using: "composite"
   steps:
-    - run: |
-        commit=a6dd85e7b13107172c0502937bec6b718002510d
+    - shell: bash
+      run: |
+        set -x
+        commit=b259de1dc97573a71470a1d71c3d83535934136b
         pip install git+https://github.com/krobelus/sphinx-markdown-builder@"$commit"
-      shell: bash
+        python -c 'import sphinx_markdown_builder'
diff --git a/doc_src/conf.py b/doc_src/conf.py
index accb26bdf..52ac617b7 100644
--- a/doc_src/conf.py
+++ b/doc_src/conf.py
@@ -16,6 +16,10 @@ from docutils import nodes
 
 try:
     import sphinx_markdown_builder
+
+    extensions = [
+        "sphinx_markdown_builder",
+    ]
 except ImportError:
     pass
 
diff --git a/tests/checks/sphinx-markdown-changelog.fish b/tests/checks/sphinx-markdown-changelog.fish
index 63924b941..6a81bf8f0 100644
--- a/tests/checks/sphinx-markdown-changelog.fish
+++ b/tests/checks/sphinx-markdown-changelog.fish
@@ -7,7 +7,10 @@ if not test -e $workspace_root/.git
     return
 end
 
-$workspace_root/build_tools/release-notes.sh -q >relnotes.md
-or echo "Failed to build Markdown release notes."
+$workspace_root/build_tools/release-notes.sh -q >?relnotes.md
+or {
+    echo "Failed to build Markdown release notes."
+    return
+}
 sed -n 1p relnotes.md | grep -q '^## fish \S* (released .*)'
 or echo "Unexpected changelog title"