diff --git a/taskcluster/ci/source-test/doc.yml b/taskcluster/ci/source-test/doc.yml
index 858361da164f..a3529aaf9e49 100644
--- a/taskcluster/ci/source-test/doc.yml
+++ b/taskcluster/ci/source-test/doc.yml
@@ -28,7 +28,7 @@ generate:
             cp -r /build/node_modules_eslint node_modules &&
             ln -s ../tools/lint/eslint/eslint-plugin-mozilla node_modules &&
             ln -s ../tools/lint/eslint/eslint-plugin-spidermonkey-js node_modules &&
-            ./mach doc --outdir docs-out --no-open --no-serve --archive --fatal-warnings --dump-trees=/builds/worker/artifacts/trees.json
+            ./mach doc --outdir docs-out --no-open --no-serve --archive --fatal-warnings --check-num-warnings --dump-trees=/builds/worker/artifacts/trees.json
         sparse-profile: sphinx-docs
     optimization:
         skip-unless-schedules: [docs]
@@ -64,7 +64,7 @@ upload:
             cp -r /build/node_modules_eslint node_modules &&
             ln -s ../tools/lint/eslint/eslint-plugin-mozilla node_modules &&
             ln -s ../tools/lint/eslint/eslint-plugin-spidermonkey-js node_modules &&
-            ./mach doc --upload --no-open --no-serve --fatal-warnings --write-url /builds/worker/firefox-source-docs-url.txt --dump-trees=/builds/worker/artifacts/trees.json
+            ./mach doc --upload --no-open --no-serve --fatal-warnings --check-num-warnings --write-url /builds/worker/firefox-source-docs-url.txt --dump-trees=/builds/worker/artifacts/trees.json
         sparse-profile: sphinx-docs
     scopes:
         - secrets:get:project/releng/gecko/build/level-{level}/gecko-docs-upload