diff --git a/packages/vat-data/test/test-prepare-revocable.js b/packages/vat-data/test/test-prepare-revocable.js
index de22c14f467d..e56bc8a2ee4e 100644
--- a/packages/vat-data/test/test-prepare-revocable.js
+++ b/packages/vat-data/test/test-prepare-revocable.js
@@ -29,7 +29,7 @@ test('test revoke defineVirtualExoClass', t => {
     baggage,
     'UpCounter',
     UpCounterI,
-    /** @param {number} x */
+    /** @param {number} [x] */
     (x = 0) => ({ x }),
     {
       incr(y = 1) {
@@ -65,7 +65,7 @@ test('test revoke defineVirtualExoClassKit', t => {
     baggage,
     'Counter',
     { up: UpCounterI, down: DownCounterI },
-    /** @param {number} x */
+    /** @param {number} [x] */
     (x = 0) => ({ x }),
     {
       up: {
diff --git a/packages/zoe/src/contractFacet/types-ambient.d.ts b/packages/zoe/src/contractFacet/types-ambient.d.ts
index d6610121400d..6ee5f3f87d30 100644
--- a/packages/zoe/src/contractFacet/types-ambient.d.ts
+++ b/packages/zoe/src/contractFacet/types-ambient.d.ts
@@ -7,6 +7,14 @@ type IssuerOptionsRecord = import('@agoric/ertp').IssuerOptionsRecord;
  */
 type Completion = any;
 type ZCFMakeEmptySeatKit = (exit?: ExitRule | undefined) => ZcfSeatKit;
+
+type MakeInvitation = <Result>(
+  offerHandler: OfferHandler<Result>,
+  description: string,
+  customDetails?: object,
+  proposalShape?: Pattern,
+) => Promise<Invitation<R, A>>;
+
 /**
  * Zoe Contract Facet
  *
@@ -54,12 +62,7 @@ type ZCF<CT extends unknown = Record<string, unknown>> = {
    * getting in the `customDetails`. `customDetails` will be
    * placed in the details of the invitation.
    */
-  makeInvitation: <Result>(
-    offerHandler: OfferHandler<Result>,
-    description: string,
-    customDetails?: object,
-    proposalShape?: Pattern,
-  ) => Promise<Invitation<R, A>>;
+  makeInvitation: MakeInvitation;
   shutdown: (completion: Completion) => void;
   shutdownWithFailure: ShutdownWithFailure;
   getZoeService: () => ERef<ZoeService>;
diff --git a/packages/zoe/src/contractSupport/prepare-ownable.js b/packages/zoe/src/contractSupport/prepare-ownable.js
index 92670ec450a6..6eaafcbe6692 100644
--- a/packages/zoe/src/contractSupport/prepare-ownable.js
+++ b/packages/zoe/src/contractSupport/prepare-ownable.js
@@ -10,9 +10,18 @@ const TransferProposalShape = M.splitRecord({
   },
 });
 
+/**
+ * @template {any} [U=any]
+ * @param {import('@agoric/vat-data').Baggage} baggage
+ * @param {MakeInvitation} makeInvitation
+ * @param {string} uKindName
+ * @param {string} uInterfaceName
+ * @param {(string|symbol)[]} uMethodNames
+ * @returns {(underlying: U) => U}
+ */
 export const prepareOwnable = (
-  zcf,
   baggage,
+  makeInvitation,
   uKindName,
   uInterfaceName,
   uMethodNames,
@@ -37,11 +46,11 @@ export const prepareOwnable = (
             revoker,
           },
         } = this;
-        const customDetails = underlying.getCustomDetails();
+        const customDetails = underlying.getInvitationCustomDetails();
         // eslint-disable-next-line no-use-before-define
         const transferHandler = makeTransferHandler(underlying);
 
-        const invitation = zcf.makeInvitation(
+        const invitation = makeInvitation(
           transferHandler,
           'transfer',
           customDetails,
diff --git a/packages/zoe/src/contracts/ownable-counter.js b/packages/zoe/test/unitTests/contracts/ownable-counter.js
similarity index 86%
rename from packages/zoe/src/contracts/ownable-counter.js
rename to packages/zoe/test/unitTests/contracts/ownable-counter.js
index ac08b66c56d7..2ca304c548af 100644
--- a/packages/zoe/src/contracts/ownable-counter.js
+++ b/packages/zoe/test/unitTests/contracts/ownable-counter.js
@@ -1,6 +1,6 @@
 import { M } from '@endo/patterns';
 import { prepareExoClassKit } from '@agoric/vat-data';
-import { prepareOwnable } from '../contractSupport/prepare-ownable.js';
+import { prepareOwnable } from '../../../src/contractSupport/prepare-ownable.js';
 
 /** @typedef {import('@agoric/vat-data').Baggage} Baggage */
 
@@ -20,7 +20,7 @@ export const start = async (zcf, privateArgs, baggage) => {
       counter: M.interface('Counter', {
         incr: M.call().returns(M.bigint()),
         // required by makePrepareOwnableClass
-        getCustomDetails: M.call().returns(
+        getInvitationCustomDetails: M.call().returns(
           harden({
             count: M.bigint(),
           }),
@@ -40,7 +40,7 @@ export const start = async (zcf, privateArgs, baggage) => {
           state.count += 1n;
           return state.count;
         },
-        getCustomDetails() {
+        getInvitationCustomDetails() {
           const {
             state: { count },
           } = this;
@@ -61,11 +61,11 @@ export const start = async (zcf, privateArgs, baggage) => {
   );
 
   const makeOwnableCounter = prepareOwnable(
-    zcf,
     baggage,
+    (...args) => zcf.makeInvitation(...args),
     'Counter',
     'OwnableCounter',
-    ['incr', 'getCustomDetails'],
+    ['incr', 'getInvitationCustomDetails'],
   );
 
   const { counter: underlyingCounter, viewer } =
diff --git a/packages/zoe/test/unitTests/contracts/test-ownable-counter.js b/packages/zoe/test/unitTests/contracts/test-ownable-counter.js
index 7484e8a60f49..f737793c5624 100644
--- a/packages/zoe/test/unitTests/contracts/test-ownable-counter.js
+++ b/packages/zoe/test/unitTests/contracts/test-ownable-counter.js
@@ -12,7 +12,7 @@ import { makeFakeVatAdmin } from '../../../tools/fakeVatAdmin.js';
 const filename = new URL(import.meta.url).pathname;
 const dirname = path.dirname(filename);
 
-const root = `${dirname}/../../../src/contracts/ownable-counter.js`;
+const root = `${dirname}/ownable-counter.js`;
 
 test('zoe - ownable-counter contract', async t => {
   const { admin: fakeVatAdmin, vatAdminState } = makeFakeVatAdmin();
@@ -44,7 +44,7 @@ test('zoe - ownable-counter contract', async t => {
   t.deepEqual(await E(firstCounter)[GET_METHOD_NAMES](), [
     '__getInterfaceGuard__',
     '__getMethodNames__',
-    'getCustomDetails',
+    'getInvitationCustomDetails',
     'incr',
     'makeTransferInvitation',
   ]);
@@ -52,7 +52,7 @@ test('zoe - ownable-counter contract', async t => {
   t.is(await E(firstCounter).incr(), 4n);
   t.is(await E(viewCounter).view(), 4n);
 
-  t.deepEqual(await E(firstCounter).getCustomDetails(), {
+  t.deepEqual(await E(firstCounter).getInvitationCustomDetails(), {
     count: 4n,
   });
 
@@ -61,12 +61,12 @@ test('zoe - ownable-counter contract', async t => {
   t.deepEqual(await E(firstCounter)[GET_METHOD_NAMES](), [
     '__getInterfaceGuard__',
     '__getMethodNames__',
-    'getCustomDetails',
+    'getInvitationCustomDetails',
     'incr',
     'makeTransferInvitation',
   ]);
 
-  await t.throwsAsync(() => E(firstCounter).getCustomDetails(), {
+  await t.throwsAsync(() => E(firstCounter).getInvitationCustomDetails(), {
     message: '"Counter_caretaker" revoked',
   });
   await t.throwsAsync(() => E(firstCounter).incr(), {
@@ -97,14 +97,14 @@ test('zoe - ownable-counter contract', async t => {
   t.is(await E(reviveCounterSeat).hasExited(), true);
 
   t.is(await E(viewCounter).view(), 4n);
-  t.deepEqual(await E(counter2).getCustomDetails(), {
+  t.deepEqual(await E(counter2).getInvitationCustomDetails(), {
     count: 4n,
   });
 
   t.is(await E(counter2).incr(), 5n);
 
   t.is(await E(viewCounter).view(), 5n);
-  t.deepEqual(await E(counter2).getCustomDetails(), {
+  t.deepEqual(await E(counter2).getInvitationCustomDetails(), {
     count: 5n,
   });
 });