diff --git a/sql/my_json_writer.cc b/sql/my_json_writer.cc
index e97db210da7..d36fdd1192a 100644
--- a/sql/my_json_writer.cc
+++ b/sql/my_json_writer.cc
@@ -330,6 +330,8 @@ void Single_line_formatting_helper::flush_on_one_line()
     ptr++;
   }
   owner->output.append(']');
+  /* We've printed out the contents of the buffer, mark it as empty */
+  buf_ptr= buffer;
 }