diff --git a/doc/zmq_msg_gets.txt b/doc/zmq_msg_gets.txt
index 5d6b3de6..73210d51 100644
--- a/doc/zmq_msg_gets.txt
+++ b/doc/zmq_msg_gets.txt
@@ -43,7 +43,7 @@ zmq_msg_t msg;
 zmq_msg_init (&msg);
 rc = zmq_msg_recv (&msg, dealer, 0);
 assert (rc != -1);
-char *user_id = zmq_msg_gets (&msg, "User-Id");
+const char *user_id = zmq_msg_gets (&msg, "User-Id");
 zmq_msg_close (&msg);
 ----