diff --git a/reference/strings/setup.xml b/reference/strings/setup.xml
index 1c0b9abb32..5a29980c31 100644
--- a/reference/strings/setup.xml
+++ b/reference/strings/setup.xml
@@ -12,6 +12,10 @@
  <section xml:id="strings.installation">
   &reftitle.install;
   &no.install;
+  <simpara>
+   As of PHP 8.1.0, <function>crypt</function> can be built against a system crypt library
+   by specifying the <option role="configure">--with-external-libcrypt</option> configure option.
+  </simpara>
  </section>
 
  <section xml:id="strings.configuration">