diff --git a/packages/fast-usdc/src/exos/transaction-feed.js b/packages/fast-usdc/src/exos/transaction-feed.js
index 87eacf07b3f..68c00ecb53c 100644
--- a/packages/fast-usdc/src/exos/transaction-feed.js
+++ b/packages/fast-usdc/src/exos/transaction-feed.js
@@ -1,6 +1,7 @@
 import { makeTracer } from '@agoric/internal';
 import { prepareDurablePublishKit } from '@agoric/notifier';
-import { M } from '@endo/patterns';
+import { keyEQ, M } from '@endo/patterns';
+import { Fail } from '@endo/errors';
 import { CctpTxEvidenceShape } from '../type-guards.js';
 import { defineInertInvitation } from '../utils/zoe.js';
 import { prepareOperatorKit } from './operator-kit.js';
@@ -127,6 +128,7 @@ export const prepareTransactionFeedKit = (zone, zcf) => {
           const { operators, pending } = this.state;
           trace('submitEvidence', operatorId, evidence);
 
+          // TODO https://github.com/Agoric/agoric-sdk/pull/10720
           // TODO validate that it's a valid for Fast USDC before accepting
           // E.g. that the `recipientAddress` is the FU settlement account and that
           // the EUD is a chain supported by FU.
@@ -161,7 +163,26 @@ export const prepareTransactionFeedKit = (zone, zcf) => {
             return;
           }
 
-          // TODO verify that all found deep equal
+          let lastEvidence;
+          for (const store of found) {
+            const next = store.get(txHash);
+            if (lastEvidence) {
+              if (keyEQ(lastEvidence, next)) {
+                lastEvidence = next;
+              } else {
+                trace(
+                  '🚨 conflicting evidence for',
+                  txHash,
+                  ':',
+                  lastEvidence,
+                  '!=',
+                  next,
+                );
+                Fail`conflicting evidence for ${txHash}`;
+              }
+            }
+            lastEvidence = next;
+          }
 
           // sufficient agreement, so remove from pending and publish
           for (const store of found) {
diff --git a/packages/fast-usdc/test/exos/transaction-feed.test.ts b/packages/fast-usdc/test/exos/transaction-feed.test.ts
index 5c5b74e094b..8f5084af0ea 100644
--- a/packages/fast-usdc/test/exos/transaction-feed.test.ts
+++ b/packages/fast-usdc/test/exos/transaction-feed.test.ts
@@ -47,6 +47,7 @@ test('happy aggregation', async t => {
   const evidenceSubscriber = feedKit.public.getEvidenceSubscriber();
 
   const { op1, op2, op3 } = await makeOperators(feedKit);
+
   const e1 = MockCctpTxEvidences.AGORIC_PLUS_OSMO();
   op1.operator.submitEvidence(e1);
   op2.operator.submitEvidence(e1);
@@ -74,6 +75,48 @@ test('happy aggregation', async t => {
   });
 });
 
+test('disagreement', async t => {
+  const feedKit = makeFeedKit();
+  const { op1, op2 } = await makeOperators(feedKit);
+  const e1 = MockCctpTxEvidences.AGORIC_PLUS_OSMO();
+  const e1bad = { ...e1, tx: { ...e1.tx, amount: 999_999_999n } };
+  assert(e1.txHash === e1bad.txHash);
+  op1.operator.submitEvidence(e1);
+
+  t.throws(() => op2.operator.submitEvidence(e1bad), {
+    message:
+      'conflicting evidence for "0xc81bc6105b60a234c7c50ac17816ebcd5561d366df8bf3be59ff387552761702"',
+  });
+});
+
+test('disagreement after publishing', async t => {
+  const feedKit = makeFeedKit();
+  const evidenceSubscriber = feedKit.public.getEvidenceSubscriber();
+  const { op1, op2, op3 } = await makeOperators(feedKit);
+  const e1 = MockCctpTxEvidences.AGORIC_PLUS_OSMO();
+  const e1bad = { ...e1, tx: { ...e1.tx, amount: 999_999_999n } };
+  assert(e1.txHash === e1bad.txHash);
+  op1.operator.submitEvidence(e1);
+  op2.operator.submitEvidence(e1);
+
+  t.like(await evidenceSubscriber.getUpdateSince(0), {
+    updateCount: 1n,
+  });
+
+  // it's simply ignored
+  t.notThrows(() => op3.operator.submitEvidence(e1bad));
+  t.like(await evidenceSubscriber.getUpdateSince(0), {
+    updateCount: 1n,
+  });
+
+  // now another op repeats the bad evidence, so it's published to the stream.
+  // It's the responsibility of the Advancer to fail because it has already processed that tx hash.
+  op1.operator.submitEvidence(e1bad);
+  t.like(await evidenceSubscriber.getUpdateSince(0), {
+    updateCount: 2n,
+  });
+});
+
 test('disabled operator', async t => {
   const feedKit = makeFeedKit();
   const { op1 } = await makeOperators(feedKit);