diff --git a/aos/json_tokenizer.cc b/aos/json_tokenizer.cc
index ac519c8..2486227 100644
--- a/aos/json_tokenizer.cc
+++ b/aos/json_tokenizer.cc
@@ -249,6 +249,10 @@
       if (!ConsumeString(&s)) {
         fprintf(stderr, "Error on line %d, expected string for field name.\n",
                 linenumber_);
+        if (Consume("}")) {
+          fprintf(stderr,
+                  "Got '}' instead.  Did you add an extra trailing ','?\n");
+        }
         return TokenType::kError;
       }
       field_name_ = ::std::move(s);