diff --git a/.github/workflows/test-build.yml b/.github/workflows/test-build.yml
index 22d3a94f8..bdd290189 100644
--- a/.github/workflows/test-build.yml
+++ b/.github/workflows/test-build.yml
@@ -225,6 +225,7 @@ jobs:
         run: |
           make config-clang
           echo "ENABLE_CCACHE := 1" >> Makefile.conf
+          echo "ENABLE_HELP_SOURCE := 1" >> Makefile.conf
           make -j$procs
 
       - name: Install doc prereqs
diff --git a/README.md b/README.md
index 78b8bfc51..e5b8d1072 100644
--- a/README.md
+++ b/README.md
@@ -281,4 +281,6 @@ It is recommended to use the `ENABLE_HELP_SOURCE` make option for Yosys builds
 that will be used to build the documentation.  This option enables source
 location tracking for passes and improves the command reference through grouping
 related commands and allowing for the documentation to link to the corresponding
-source files.
+source files.  Without this, a warning will be raised during the Sphinx build
+about `Found commands assigned to group unknown` and `make docs` is configured
+to fail on warnings by default.