diff --git a/spec/registry.xml b/spec/registry.xml
index 25fff3695a..be14dcae91 100644
--- a/spec/registry.xml
+++ b/spec/registry.xml
@@ -46,6 +46,11 @@
           such as "Asia/Shanghai", "Asia/Kolkata", "America/New_York".
         </description>
       </option>
+      <option name="hourCycle" values="h11 h12 h23 h24">
+        <description>
+          The hour cycle to use.
+        </description>
+      </option>
     </formatSignature>
 
     <!-- TODO: clarify if this is OK or if it is an abuse.