diff --git a/contract/,tx.json b/contract/,tx.json
deleted file mode 100644
index e69de29b..00000000
diff --git a/contract/package.json b/contract/package.json
index 2d5403ce..fe6392cf 100644
--- a/contract/package.json
+++ b/contract/package.json
@@ -54,6 +54,7 @@
     "@agoric/governance": "^0.10.4-u14.0",
     "@agoric/inter-protocol": "0.16.2-u14.1",
     "@agoric/vats": "0.15.2-u14.0",
+    "@agoric/vat-data": "0.5.3-u14.0",
     "@agoric/zoe": "^0.26.3-u14.0",
     "@endo/bundle-source": "^2.8.0",
     "@endo/far": "^0.2.22",
diff --git a/contract/src/swaparoo.contract.js b/contract/src/swaparoo.contract.js
index cf393b2e..dcccb8aa 100644
--- a/contract/src/swaparoo.contract.js
+++ b/contract/src/swaparoo.contract.js
@@ -15,6 +15,7 @@ import {
 import { ParamTypes } from '@agoric/governance/src/constants.js';
 import { CONTRACT_ELECTORATE } from '@agoric/governance/src/contractGovernance/governParam.js';
 import { handleParamGovernance } from '@agoric/governance/src/contractHelper.js';
+import { provide } from '@agoric/vat-data';
 import { makeCollectFeesInvitation } from './collectFees.js';
 import { fixHub } from './fixHub.js';
 
@@ -121,6 +122,18 @@ export const start = async (zcf, privateArgs, baggage) => {
   // TODO: update with Fee param
   const feeShape = makeNatAmountShape(feeBrand, params.getFee().value);
 
+  const generateOfferNonce = (() => {
+    // Provide the nonce durably so it can stay unique if contract upgrades.
+    // See: https://docs.agoric.com/guides/zoe/contract-upgrade.html#durability
+    let offerNonce = provide(baggage, 'offerNonce', () => -1);
+
+    return () => {
+      offerNonce += 1;
+      baggage.set('offerNonce', offerNonce);
+      return offerNonce;
+    };
+  })();
+
   /**
    * @param { ZCFSeat } firstSeat
    * @param {{ addr: string }} offerArgs
@@ -158,9 +171,10 @@ export const start = async (zcf, privateArgs, baggage) => {
       return swapWithFee(zcf, firstSeat, secondSeat, feeSeat, params.getFee());
     };
 
+    const description = `matchOffer-${generateOfferNonce()}`;
     const secondSeatInvitation = await zcf.makeInvitation(
       secondSeatOfferHandler,
-      'matchOffer',
+      description,
       { give: give1, want: want1 }, // "give" and "want" are from the proposer's perspective
     );
 
diff --git a/contract/test/snapshots/test-swap-wallet.js.md b/contract/test/snapshots/test-swap-wallet.js.md
index 9d356e00..2e20c53d 100644
--- a/contract/test/snapshots/test-swap-wallet.js.md
+++ b/contract/test/snapshots/test-swap-wallet.js.md
@@ -49,7 +49,7 @@ Generated by [AVA](https://avajs.dev).
     {
       id: 'jack-123',
       invitationSpec: {
-        description: 'matchOffer',
+        description: 'matchOffer-0',
         instance: Object @Alleged: InstanceHandle {},
         source: 'purse',
       },
diff --git a/contract/test/snapshots/test-swap-wallet.js.snap b/contract/test/snapshots/test-swap-wallet.js.snap
index b8134522..de8f920a 100644
Binary files a/contract/test/snapshots/test-swap-wallet.js.snap and b/contract/test/snapshots/test-swap-wallet.js.snap differ
diff --git a/contract/test/test-swap-wallet.js b/contract/test/test-swap-wallet.js
index 675c84d4..16dbe219 100644
--- a/contract/test/test-swap-wallet.js
+++ b/contract/test/test-swap-wallet.js
@@ -161,6 +161,7 @@ const startAlice = async (
  * @param {MockWallet} wallet
  * @param {Amount} beansAmount
  * @param {Amount} cowsAmount
+ * @param {string} offerDescription
  * @param {boolean} [jackPays]
  */
 const startJack = async (
@@ -169,6 +170,7 @@ const startJack = async (
   wallet,
   beansAmount,
   cowsAmount,
+  offerDescription,
   jackPays = false,
 ) => {
   const instance = wellKnown.instance[contractName];
@@ -188,7 +190,7 @@ const startJack = async (
     invitationSpec: {
       source: 'purse',
       instance,
-      description: 'matchOffer',
+      description: offerDescription,
     },
     proposal,
   };
@@ -278,7 +280,14 @@ test.serial('basic swap', async t => {
     await E(E.get(bldIssuerKit).mint).mintPayment(cowAmount),
   );
   const jackSeat = seatLike(
-    await startJack(t, wellKnown, wallet.jack, fiveBeans, cowAmount),
+    await startJack(
+      t,
+      wellKnown,
+      wallet.jack,
+      fiveBeans,
+      cowAmount,
+      'matchOffer-0',
+    ),
   );
 
   const jackPayouts = await jackSeat.getPayoutAmounts();
diff --git a/yarn.lock b/yarn.lock
index 5c9807b1..266777ea 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -8453,7 +8453,7 @@ eslint@^8.47.0, eslint@^8.56.0:
     strip-ansi "^6.0.1"
     text-table "^0.2.0"
 
-esm@agoric-labs/esm#Agoric-built, "esm@github:agoric-labs/esm#Agoric-built":
+esm@agoric-labs/esm#Agoric-built:
   version "3.2.25"
   resolved "https://codeload.github.com/agoric-labs/esm/tar.gz/3603726ad4636b2f865f463188fcaade6375638e"