diff --git a/app/static/js/vault.js b/app/static/js/vault.js
index 77059a8..a910243 100644
--- a/app/static/js/vault.js
+++ b/app/static/js/vault.js
@@ -393,6 +393,10 @@ const Vault = (() => {
    * Returns an array suitable for the shared_updates field of PUT /api/vault/<id>.
    */
   async function buildSharedUpdates(itemId, plainData, itemName) {
+    // Ensure the owner's ECDH private key is loaded before attempting re-encryption.
+    // The session may not be ready yet if the user edits before loadSharedItemsForVault
+    // completes (async race on first load).
+    await ensureSharingSession();
     if (!SharingSession.isReady()) return [];
     try {
       const res = await apiFetch("/api/sharing");