diff --git a/packages/cosmic-proto/test/helpers.test-d.ts b/packages/cosmic-proto/test/helpers.test-d.ts
index 63933043cb8..dbeafd4af4b 100644
--- a/packages/cosmic-proto/test/helpers.test-d.ts
+++ b/packages/cosmic-proto/test/helpers.test-d.ts
@@ -69,6 +69,5 @@ import type { Timestamp } from '../src/codegen/google/protobuf/timestamp.js';
     null as any;
   expectType<Timestamp>(response.completionTime);
   const responseJson: JsonSafe<typeof response> = null as any;
-  // FIXME: should be a string. UNTIL: github.com/cosmology-tech/telescope/pull/632
-  expectType<bigint>(responseJson.completionTime.seconds);
+  expectType<string>(responseJson.completionTime.seconds);
 }
diff --git a/packages/orchestration/src/exos/local-orchestration-account.js b/packages/orchestration/src/exos/local-orchestration-account.js
index a17c4d4063c..7fda8a8733b 100644
--- a/packages/orchestration/src/exos/local-orchestration-account.js
+++ b/packages/orchestration/src/exos/local-orchestration-account.js
@@ -387,8 +387,10 @@ export const prepareLocalOrchestrationAccountKit = (
        */
       queryBalancesWatcher: {
         /**
-         * @param {ResponseTo<
-         *   TypedJson<'/cosmos.bank.v1beta1.QueryAllBalancesRequest'>
+         * @param {JsonSafe<
+         *   ResponseTo<
+         *     TypedJson<'/cosmos.bank.v1beta1.QueryAllBalancesRequest'>
+         *   >
          * >} result
          * @returns {DenomAmount[]}
          */
diff --git a/packages/orchestration/src/typeGuards.js b/packages/orchestration/src/typeGuards.js
index 4c3255dbbdf..deb4ea802c9 100644
--- a/packages/orchestration/src/typeGuards.js
+++ b/packages/orchestration/src/typeGuards.js
@@ -160,8 +160,11 @@ export const chainFacadeMethods = harden({
 /**
  * for google/protobuf/timestamp.proto, not to be confused with TimestampShape
  * from `@agoric/time`
+ *
+ * `seconds` is a big integer but since it goes through JSON it is encoded as
+ * string
  */
-export const TimestampProtoShape = { seconds: M.nat(), nanos: M.number() };
+export const TimestampProtoShape = { seconds: M.string(), nanos: M.number() };
 
 /**
  * see {@link TxBody} for more details
diff --git a/packages/vats/tools/fake-bridge.js b/packages/vats/tools/fake-bridge.js
index 32e3ee6575c..36c39af8d37 100644
--- a/packages/vats/tools/fake-bridge.js
+++ b/packages/vats/tools/fake-bridge.js
@@ -218,7 +218,7 @@ export const fakeLocalChainBridgeTxMsgHandler = (message, sequence) => {
     case '/cosmos.staking.v1beta1.MsgUndelegate': {
       return /** @type {JsonSafe<MsgUndelegateResponse>} */ ({
         // 5 seconds from unix epoch
-        completionTime: { seconds: 5n, nanos: 0 },
+        completionTime: { seconds: '5', nanos: 0 },
       });
     }
     // returns one empty object per message unless specified