diff --git a/SWIPs/swip-39.md b/SWIPs/swip-39.md
index 930ff0cd..238e9143 100644
--- a/SWIPs/swip-39.md
+++ b/SWIPs/swip-39.md
@@ -195,6 +195,8 @@ sequenceDiagram
     participant Trie
 
     Client->>Registry: Register(a)
+    Registry-->>Client: ack
+    Client->>Registry: GetPrefix(a)
     Registry-->>Client: prefix
     Client->>Registry: Validate(a,o)
     Registry->>Trie: update(F,E)