diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 7dc8150..ca3331b 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -129,10 +129,16 @@ jobs:
       - name: Build the documentation
         working-directory: linux-i2c
         run: |
-          sudo apt-get install -y python3-sphinx python3-sphinx-rtd-theme
+          sudo apt-get install -y graphviz python3-sphinx python3-sphinx-rtd-theme
           cp ../docs/submission/i2c-imc-skylake.rst Documentation/i2c/busses/
           sed -i 's|^   i2c-i801$|   i2c-i801\n   i2c-imc-skylake|' \
             Documentation/i2c/busses/index.rst
           grep -q i2c-imc-skylake Documentation/i2c/busses/index.rst
           make O=../linux-out htmldocs SPHINXDIRS=i2c 2>&1 | tee doc.log | tail -20
-          ! grep -Ei 'WARNING|ERROR' doc.log
+          # Only diagnostics naming this file should fail the job. The docs
+          # build emits environment-dependent warnings that say nothing about
+          # this patch.
+          if grep -Ei 'warning|error' doc.log | grep -i i2c-imc-skylake; then
+            echo "the documentation build complained about this file" >&2
+            exit 1
+          fi