diff --git a/docs/tutorial-01-wget.md b/docs/tutorial-01-wget.md
index 86a2c47257..2a5514f524 100644
--- a/docs/tutorial-01-wget.md
+++ b/docs/tutorial-01-wget.md
@@ -61,7 +61,7 @@ void wget_callback(WFHttpTask *task)
     ...
 
     // print response body to stdin
-    void *body;
+    const void *body;
     size_t body_len;
     resp->get_parsed_body(&body, &body_len); // always success.
     fwrite(body, 1, body_len, stdout);