diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1d660aa04..5702640dc 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,10 @@
 
 All notable changes to the Movement TypeScript SDK will be captured in this file. This changelog is written by hand for now. It adheres to the format set out by [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
+# Unreleased
+
+- Report an expired transaction as expired. `waitForTransaction` retries a 404, so once a node drops an expired transaction from its mempool the wait kept polling a hash that no longer existed and ended with "timed out in pending state", which points at `timeoutSecs` when no amount of waiting can help. It now compares the transaction's `expiration_timestamp_secs` against the ledger timestamp and says the transaction expired, naming `options.expireTimestamp` and `transactionGenerationConfig.defaultTxnExpirySecFromNow` as the ways to widen the window.
+
 # 5.1.7 (2026-03-25)
 
 - Add mainnet Movement Name Service (MNS) router contract address to `NetworkToMnsContract`, enabling `movement.mns` on `Network.MAINNET`.
diff --git a/src/internal/transaction.ts b/src/internal/transaction.ts
index 9e6089cda..a52629f4c 100644
--- a/src/internal/transaction.ts
+++ b/src/internal/transaction.ts
@@ -26,7 +26,7 @@ import {
 import { DEFAULT_TXN_TIMEOUT_SEC, ProcessorType } from "../utils/const";
 import { sleep } from "../utils/helpers";
 import { memoizeAsync } from "../utils/memoize";
-import { getIndexerLastSuccessVersion, getProcessorStatus } from "./general";
+import { getIndexerLastSuccessVersion, getLedgerInfo, getProcessorStatus } from "./general";
 
 /**
  * Retrieve a list of transactions based on the specified options.
@@ -147,6 +147,30 @@ export async function isTransactionPending(args: {
   }
 }
 
+/**
+ * Whether a transaction's expiry has already passed on chain.
+ *
+ * `expiration_timestamp_secs` is in seconds and `ledger_timestamp` is in
+ * microseconds, so the two need converting before they can be compared.
+ *
+ * Chain time rather than local time on purpose: the node decides what has
+ * expired, and a caller with a skewed clock would otherwise be told the wrong
+ * thing about a transaction that is still perfectly valid.
+ *
+ * @group Implementation
+ */
+export function hasTransactionExpired(args: {
+  expirationTimestampSecs: string | number | bigint;
+  ledgerTimestampMicros: string | number | bigint;
+}): boolean {
+  const expirySecs = Number(args.expirationTimestampSecs);
+  const ledgerSecs = Number(args.ledgerTimestampMicros) / 1_000_000;
+  if (!Number.isFinite(expirySecs) || !Number.isFinite(ledgerSecs)) {
+    return false;
+  }
+  return ledgerSecs > expirySecs;
+}
+
 /**
  * Waits for a transaction to be confirmed by its hash.
  * This function allows you to monitor the status of a transaction until it is finalized.
@@ -180,7 +204,7 @@ export async function longWaitForTransaction(args: {
  * @param args.options.timeoutSecs - The maximum time to wait for the transaction in seconds. Defaults to a predefined value.
  * @param args.options.checkSuccess - A flag indicating whether to check the success status of the transaction. Defaults to true.
  * @returns A promise that resolves to the transaction response once the transaction is confirmed.
- * @throws WaitForTransactionError if the transaction times out or remains pending.
+ * @throws WaitForTransactionError if the transaction expires on chain, or times out while still pending.
  * @throws FailedTransactionError if the transaction fails.
  * @group Implementation
  */
@@ -276,6 +300,31 @@ export async function waitForTransaction(args: {
   }
 
   if (lastTxn.type === TransactionResponseType.Pending) {
+    // A dropped transaction and a slow one are indistinguishable from the poll
+    // alone: once the node garbage-collects an expired transaction the hash
+    // 404s, which is retried as if it were merely not visible yet, and the wait
+    // ends reporting a timeout. That points at timeoutSecs, when no amount of
+    // waiting can help. Ask the chain what time it is and say which one it was.
+    let expired = false;
+    try {
+      const ledgerInfo = await getLedgerInfo({ movementConfig });
+      expired = hasTransactionExpired({
+        expirationTimestampSecs: lastTxn.expiration_timestamp_secs,
+        ledgerTimestampMicros: ledgerInfo.ledger_timestamp,
+      });
+    } catch {
+      // Best effort. If the node cannot be reached for the timestamp, fall back
+      // to the original message rather than replacing one unclear failure with
+      // another.
+    }
+    if (expired) {
+      throw new WaitForTransactionError(
+        `Transaction ${transactionHash} expired at ${lastTxn.expiration_timestamp_secs} and was dropped from the mempool. ` +
+          `It will never commit. Resubmit with a longer expiry: pass options.expireTimestamp, or raise ` +
+          `transactionGenerationConfig.defaultTxnExpirySecFromNow on MovementConfig.`,
+        lastTxn,
+      );
+    }
     throw new WaitForTransactionError(
       `Transaction ${transactionHash} timed out in pending state after ${timeoutSecs} seconds`,
       lastTxn,
diff --git a/tests/unit/transactionExpiry.test.ts b/tests/unit/transactionExpiry.test.ts
new file mode 100644
index 000000000..0c847cc62
--- /dev/null
+++ b/tests/unit/transactionExpiry.test.ts
@@ -0,0 +1,66 @@
+// Copyright © Move Industries
+// SPDX-License-Identifier: Apache-2.0
+
+import { hasTransactionExpired } from "../../src/internal/transaction";
+
+/**
+ * A transaction whose expiry has passed is dropped from the mempool, and its
+ * hash then 404s. waitForTransaction retries a 404, so it cannot tell that case
+ * apart from a transaction that is simply slow, and reports a poll timeout for
+ * both. This is the comparison that separates them.
+ *
+ * The two fields are in different units: expiration_timestamp_secs is seconds,
+ * ledger_timestamp is microseconds.
+ */
+describe("hasTransactionExpired", () => {
+  const expirySecs = "1786000000";
+  const asMicros = (secs: number) => String(secs * 1_000_000);
+
+  it("reports expired when chain time has passed the expiry", () => {
+    expect(
+      hasTransactionExpired({
+        expirationTimestampSecs: expirySecs,
+        ledgerTimestampMicros: asMicros(1786000001),
+      }),
+    ).toBe(true);
+  });
+
+  it("reports not expired when chain time is before the expiry", () => {
+    expect(
+      hasTransactionExpired({
+        expirationTimestampSecs: expirySecs,
+        ledgerTimestampMicros: asMicros(1785999999),
+      }),
+    ).toBe(false);
+  });
+
+  it("treats the exact expiry second as not yet expired", () => {
+    expect(
+      hasTransactionExpired({
+        expirationTimestampSecs: expirySecs,
+        ledgerTimestampMicros: asMicros(1786000000),
+      }),
+    ).toBe(false);
+  });
+
+  it("converts units rather than comparing the numbers directly", () => {
+    // Compared raw, a microsecond ledger timestamp dwarfs any second-based
+    // expiry and every transaction looks expired.
+    expect(
+      hasTransactionExpired({
+        expirationTimestampSecs: expirySecs,
+        ledgerTimestampMicros: asMicros(1000),
+      }),
+    ).toBe(false);
+  });
+
+  it("accepts numbers and bigints as well as the strings the API returns", () => {
+    expect(hasTransactionExpired({ expirationTimestampSecs: 100, ledgerTimestampMicros: 200_000_000 })).toBe(true);
+    expect(hasTransactionExpired({ expirationTimestampSecs: 100n, ledgerTimestampMicros: 50_000_000n })).toBe(false);
+  });
+
+  it("reports not expired on unparseable input, so a bad value cannot invent an expiry", () => {
+    expect(hasTransactionExpired({ expirationTimestampSecs: "not-a-number", ledgerTimestampMicros: "1" })).toBe(false);
+    expect(hasTransactionExpired({ expirationTimestampSecs: "1", ledgerTimestampMicros: "not-a-number" })).toBe(false);
+  });
+});