diff --git a/docs/topics/rosbag1.rst b/docs/topics/rosbag1.rst
index bbae2eb4..0e9b7c94 100644
--- a/docs/topics/rosbag1.rst
+++ b/docs/topics/rosbag1.rst
@@ -22,6 +22,7 @@ Instances of the :py:class:`Writer <rosbags.rosbag1.Writer>` class can create an
 
        # serialize and write message
        message = String('hello world')
+       timestamp = 42
        writer.write(connection, timestamp, cdr_to_ros1(serialize_cdr(message, msgtype), msgtype))
 
 Reading rosbag1
diff --git a/docs/topics/rosbag2.rst b/docs/topics/rosbag2.rst
index 3e788bb3..1f3fbe57 100644
--- a/docs/topics/rosbag2.rst
+++ b/docs/topics/rosbag2.rst
@@ -37,6 +37,7 @@ Instances of the :py:class:`Writer <rosbags.rosbag2.Writer>` class can create an
        connection = writer.add_connection(topic, msgtype, 'cdr', '')
 
        # serialize and write message
+       timestamp = 42
        message = String('hello world')
        writer.write(connection, timestamp, serialize_cdr(message, msgtype))