diff --git a/packages/exo/test/make-legacy-guards.js b/packages/exo/test/make-legacy-guards.js
new file mode 100644
index 0000000000..e366fd86fd
--- /dev/null
+++ b/packages/exo/test/make-legacy-guards.js
@@ -0,0 +1,29 @@
+/**
+ * @param {import('@endo/patterns').AwaitArgGuardPayload} payload
+ */
+export const makeLegacyAwaitArgGuard = payload =>
+  harden({
+    klass: 'awaitArg',
+    ...payload,
+  });
+harden(makeLegacyAwaitArgGuard);
+
+/**
+ * @param {import('@endo/patterns').MethodGuardPayload} payload
+ */
+export const makeLegacyMethodGuard = payload =>
+  harden({
+    klass: 'methodGuard',
+    ...payload,
+  });
+harden(makeLegacyMethodGuard);
+
+/**
+ * @param {import('@endo/patterns').InterfaceGuardPayload} payload
+ */
+export const makeLegacyInterfaceGuard = payload =>
+  harden({
+    klass: 'Interface',
+    ...payload,
+  });
+harden(makeLegacyInterfaceGuard);
diff --git a/packages/exo/test/test-legacy-guard-tolerance.js b/packages/exo/test/test-legacy-guard-tolerance.js
new file mode 100644
index 0000000000..d2377a2246
--- /dev/null
+++ b/packages/exo/test/test-legacy-guard-tolerance.js
@@ -0,0 +1,140 @@
+// @ts-check
+// eslint-disable-next-line import/order
+import { test } from './prepare-test-env-ava.js';
+
+import { passStyleOf } from '@endo/pass-style';
+import {
+  M,
+  getAwaitArgGuardPayload,
+  getInterfaceGuardPayload,
+  getMethodGuardPayload,
+} from '@endo/patterns';
+import {
+  makeLegacyAwaitArgGuard,
+  makeLegacyMethodGuard,
+  makeLegacyInterfaceGuard,
+} from './make-legacy-guards.js';
+import { makeExo } from '../src/exo-makers.js';
+
+test('legacy guard tolerance', async t => {
+  const aag = M.await(88);
+  const laag = makeLegacyAwaitArgGuard({
+    argGuard: 88,
+  });
+  const mg1 = M.callWhen(77, aag).returns(M.any());
+  const mg2 = M.callWhen(77, laag).returns(M.any());
+  const lmg = makeLegacyMethodGuard({
+    callKind: 'async',
+    argGuards: [77, laag],
+    returnGuard: M.any(),
+  });
+  const ig1 = M.interface('Foo', {
+    mg1,
+    mg2,
+  });
+  const lig = makeLegacyInterfaceGuard({
+    interfaceName: 'Foo',
+    methodGuards: {
+      mg1,
+      mg2,
+      // @ts-expect-error Legacy adaptor can be ill typed
+      lmg,
+    },
+  });
+  t.is(passStyleOf(laag), 'copyRecord');
+  t.is(passStyleOf(lmg), 'copyRecord');
+  t.is(passStyleOf(lig), 'copyRecord');
+
+  t.deepEqual(getAwaitArgGuardPayload(aag), {
+    argGuard: 88,
+  });
+  // @ts-expect-error Legacy adaptor can be ill typed
+  t.throws(() => getAwaitArgGuardPayload(laag), {
+    message:
+      'awaitArgGuard: copyRecord {"argGuard":88,"klass":"awaitArg"} - Must be a guard:awaitArgGuard',
+  });
+
+  t.deepEqual(getMethodGuardPayload(mg1), {
+    callKind: 'async',
+    argGuards: [77, aag],
+    optionalArgGuards: undefined,
+    restArgGuard: undefined,
+    returnGuard: M.any(),
+  });
+  t.deepEqual(getMethodGuardPayload(mg2), {
+    callKind: 'async',
+    argGuards: [77, laag],
+    optionalArgGuards: undefined,
+    restArgGuard: undefined,
+    returnGuard: M.any(),
+  });
+  // @ts-expect-error Legacy adaptor can be ill typed
+  t.throws(() => getMethodGuardPayload(lmg), {
+    message:
+      'methodGuard: copyRecord {"argGuards":[77,{"argGuard":88,"klass":"awaitArg"}],"callKind":"async","klass":"methodGuard","returnGuard":"[match:any]"} - Must be a guard:methodGuard',
+  });
+
+  t.deepEqual(getInterfaceGuardPayload(ig1), {
+    interfaceName: 'Foo',
+    methodGuards: {
+      mg1,
+      mg2,
+    },
+    defaultGuards: undefined,
+  });
+  // would have been ig2 if it could be made
+  t.throws(
+    () =>
+      M.interface('Foo', {
+        mg1,
+        mg2,
+        // @ts-expect-error Legacy adaptor can be ill typed
+        lmg,
+      }),
+    {
+      message:
+        'interfaceGuard: guard:interfaceGuard: methodGuards: lmg: [1]: copyRecord {"argGuards":[77,{"argGuard":88,"klass":"awaitArg"}],"callKind":"async","klass":"methodGuard","returnGuard":"[match:any]"} - Must be a guard:methodGuard',
+    },
+  );
+  // @ts-expect-error Legacy adaptor can be ill typed
+  t.throws(() => getInterfaceGuardPayload(lig), {
+    message:
+      'interfaceGuard: copyRecord {"interfaceName":"Foo","klass":"Interface","methodGuards":{"lmg":{"argGuards":[77,{"argGuard":88,"klass":"awaitArg"}],"callKind":"async","klass":"methodGuard","returnGuard":"[match:any]"},"mg1":"[guard:methodGuard]","mg2":"[guard:methodGuard]"}} - Must be a guard:interfaceGuard',
+  });
+
+  const { meth } = {
+    meth: (x, y) => [x, y],
+  };
+
+  const f1 = makeExo('foo', ig1, {
+    mg1: meth,
+    mg2: meth,
+  });
+  t.deepEqual(await f1.mg1(77, 88), [77, 88]);
+  await t.throwsAsync(async () => f1.mg1(77, laag), {
+    message:
+      'In "mg1" method of (foo): arg 1: {"argGuard":88,"klass":"awaitArg"} - Must be: 88',
+  });
+  await t.throwsAsync(async () => f1.mg2(77, 88), {
+    message:
+      'In "mg2" method of (foo): arg 1: 88 - Must be: {"argGuard":88,"klass":"awaitArg"}',
+  });
+  t.deepEqual(await f1.mg2(77, laag), [77, laag]);
+
+  t.throws(
+    () =>
+      makeExo(
+        'foo',
+        // @ts-expect-error Legacy adaptor can be ill typed
+        lig,
+        {
+          mg1: meth,
+          mg2: meth,
+        },
+      ),
+    {
+      message:
+        'interfaceGuard: copyRecord {"interfaceName":"Foo","klass":"Interface","methodGuards":{"lmg":{"argGuards":[77,{"argGuard":88,"klass":"awaitArg"}],"callKind":"async","klass":"methodGuard","returnGuard":"[match:any]"},"mg1":"[guard:methodGuard]","mg2":"[guard:methodGuard]"}} - Must be a guard:interfaceGuard',
+    },
+  );
+});