diff --git a/.github/workflows/phpunit.yml b/.github/workflows/phpunit.yml
index 367ae8c4a5..af1857e0b6 100644
--- a/.github/workflows/phpunit.yml
+++ b/.github/workflows/phpunit.yml
@@ -22,6 +22,10 @@ jobs:
     env:
       WP_MULTISITE: ${{ matrix.multisite }}
     strategy:
+      # Report every matrix leg's own result rather than the default fail-fast
+      # cancelling the others as soon as one fails - same reasoning as cypress.yml's
+      # `fail-fast: false`.
+      fail-fast: false
       matrix:
         include:
           - php: 7.4
@@ -30,6 +34,9 @@ jobs:
           - php: 8.0
             wordpress: 6.9
             multisite: 0
+          - php: 8.0
+            wordpress: trunk
+            multisite: 0
 
     name: PHP ${{ matrix.php }} tests in WP ${{ matrix.wordpress }}
     steps:
@@ -53,6 +60,33 @@ jobs:
           sed -i "s/youremptytestdbnamehere/wordpress_tests/" wp-tests-config.php
           sed -i "s/yourusernamehere/root/" wp-tests-config.php
           sed -i "s/yourpasswordhere/root/" wp-tests-config.php
+
+      # A release branch (e.g. 6.9) ships pre-built dist/minified assets under `src/`;
+      # a raw `trunk` checkout doesn't, so it hits unrelated core code paths that
+      # expect them to already exist (wp_maybe_inline_styles's dist stylesheet check,
+      # wp-admin CSS minification for e.g. view-transitions.min.css). Build them the
+      # same way core's own CI does (reusable-build-package.yml: npm ci && npm run
+      # build), but with the `:dev` variant so the output lands in `src/` (Gruntfile's
+      # WORKING_DIR under `--dev`) where WP_DEVELOP_DIR points, instead of the plain
+      # build's separate `build/` package directory.
+      #
+      # Node version comes from the WP core checkout's own `.nvmrc`, not this
+      # runner's default - core's `engines.node` requirement moves with trunk and the
+      # runner default (Node 22 as of this writing) already trails it (WordPress#7.2.0
+      # requires >=24.18.0).
+      - name: Set up Node for WP core's build (trunk only)
+        if: matrix.wordpress == 'trunk'
+        uses: actions/setup-node@v4
+        with:
+          node-version-file: /tmp/wordpress/.nvmrc
+
+      - name: Build WP core assets (trunk only - release branches ship these pre-built)
+        if: matrix.wordpress == 'trunk'
+        timeout-minutes: 5
+        run: |
+          cd /tmp/wordpress
+          npm ci
+          npm run build:dev
       - name: Creating database
         run: |
           sudo /etc/init.d/mysql start
diff --git a/tests/phpunit/styles/test_FrmStylesController.php b/tests/phpunit/styles/test_FrmStylesController.php
index d4061d4bdb..e5697569a0 100644
--- a/tests/phpunit/styles/test_FrmStylesController.php
+++ b/tests/phpunit/styles/test_FrmStylesController.php
@@ -22,6 +22,15 @@ public function test_front_head() {
 		ob_start();
 		wp_head();
 		$styles = ob_get_clean();
+
+		// wp_maybe_inline_styles() (WP core, unrelated to anything Formidable enqueues)
+		// flags a core stylesheet's dist asset as unreadable whenever this environment's
+		// WP checkout doesn't have its built dist/ files on disk - a property of the
+		// checkout, not the WP version under test, so a released-branch job may never
+		// see it while an unbuilt trunk checkout always does. Discard it either way
+		// rather than requiring it to fire.
+		unset( $this->caught_doing_it_wrong['wp_maybe_inline_styles'] );
+
 		$this->assertNotEmpty( $styles );
 
 		$frm_settings    = FrmAppHelper::get_settings();