diff --git a/nixos/doc/manual/release-notes/rl-1909.xml b/nixos/doc/manual/release-notes/rl-1909.xml
index 6c958583993..5d4a7b2848d 100644
--- a/nixos/doc/manual/release-notes/rl-1909.xml
+++ b/nixos/doc/manual/release-notes/rl-1909.xml
@@ -112,6 +112,19 @@
       </link>
     </para>
    </listitem>
+   <listitem>
+     <para>
+     IPv6 Privacy Extensions are now enabled by default for undeclared
+     interfaces. The previous behaviour was quite misleading — even though
+     the default value for
+     <option>networking.interfaces.*.preferTempAddress</option> was
+     <literal>true</literal>, undeclared interfaces would not prefer temporary
+     addresses. Now, interfaces not mentioned in the config will prefer
+     temporary addresses. EUI64 addresses can still be set as preferred by
+     explicitly setting the option to <literal>false</literal> for the
+     interface in question.
+    </para>
+   </listitem>
    <listitem>
     <para>
      Since Bittorrent Sync was superseded by Resilio Sync in 2016, the