diff --git a/doc/api/url.md b/doc/api/url.md
index 82a5e1d3a0fbe4..11b37a4f8369d2 100644
--- a/doc/api/url.md
+++ b/doc/api/url.md
@@ -913,6 +913,9 @@ invalid domain, the empty string is returned.
 
 It performs the inverse operation to [`url.domainToUnicode()`][].
 
+This feature is only available if the `node` executable was compiled with
+[ICU][] enabled. If not, the domain names are passed through unchanged.
+
 ```js
 const url = require('url');
 console.log(url.domainToASCII('español.com'));
@@ -938,6 +941,9 @@ domain, the empty string is returned.
 
 It performs the inverse operation to [`url.domainToASCII()`][].
 
+This feature is only available if the `node` executable was compiled with
+[ICU][] enabled. If not, the domain names are passed through unchanged.
+
 ```js
 const url = require('url');
 console.log(url.domainToUnicode('xn--espaol-zwa.com'));