diff --git a/book.json b/book.json
index a563184868ac..2beadd31a8c3 100644
--- a/book.json
+++ b/book.json
@@ -25,7 +25,7 @@
       "etoc": {
         "maxdepth": 3,
         "notoc": true
-      }
+      },
       "toolbar": {
         "buttons": [
           {