diff --git a/src/acp/translator.lifecycle.test.ts b/src/acp/translator.lifecycle.test.ts
index 3b7c847cfa7..5736f916330 100644
--- a/src/acp/translator.lifecycle.test.ts
+++ b/src/acp/translator.lifecycle.test.ts
@@ -254,6 +254,33 @@ describe("acp translator stable lifecycle handlers", () => {
     sessionStore.clearAllSessionsForTest();
   });
 
+  it("lists Gateway sessions with invalid updated timestamps", async () => {
+    const request = vi.fn(async (method: string) => {
+      if (method === "sessions.list") {
+        return createGatewaySessions([
+          createSessionRow({
+            key: "agent:main:work",
+            cwd: "/tmp/openclaw",
+            title: "Work session",
+            updatedAt: Number.POSITIVE_INFINITY,
+          }),
+        ]);
+      }
+      return { ok: true };
+    }) as GatewayClient["request"];
+    const sessionStore = createInMemorySessionStore();
+    const agent = new AcpGatewayAgent(createAcpConnection(), createAcpGateway(request), {
+      sessionStore,
+    });
+
+    const result = await agent.listSessions(createListSessionsRequest({ cwd: "/tmp/openclaw" }));
+
+    expect(result.sessions).toHaveLength(1);
+    expect(result.sessions[0]?.updatedAt).toBeUndefined();
+
+    sessionStore.clearAllSessionsForTest();
+  });
+
   it("rejects session/list cursors when the cwd filter changes", async () => {
     const allRows = [
       createSessionRow({ key: "agent:main:a1", cwd: "/work/a", title: "A1" }),
diff --git a/src/acp/translator.ts b/src/acp/translator.ts
index 5deda746831..230894663f6 100644
--- a/src/acp/translator.ts
+++ b/src/acp/translator.ts
@@ -42,6 +42,7 @@ import {
   resolveFixedWindowRateLimitInteger,
   type FixedWindowRateLimiter,
 } from "../infra/fixed-window-rate-limit.js";
+import { timestampMsToIsoString } from "../shared/number-coercion.js";
 import { normalizeOptionalString } from "../shared/string-coerce.js";
 import { shortenHomePath } from "../utils.js";
 import {
@@ -502,10 +503,7 @@ function buildSessionMetadata(params: {
     normalizeOptionalString(params.row?.displayName) ||
     normalizeOptionalString(params.row?.label) ||
     params.sessionKey;
-  const updatedAt =
-    typeof params.row?.updatedAt === "number" && Number.isFinite(params.row.updatedAt)
-      ? new Date(params.row.updatedAt).toISOString()
-      : null;
+  const updatedAt = timestampMsToIsoString(params.row?.updatedAt) ?? null;
   return {
     title,
     updatedAt,
@@ -1914,7 +1912,7 @@ export class AcpGatewayAgent implements Agent {
       sessionId: session.key,
       cwd,
       title: session.derivedTitle ?? session.displayName ?? session.label ?? session.key,
-      updatedAt: session.updatedAt ? new Date(session.updatedAt).toISOString() : undefined,
+      updatedAt: timestampMsToIsoString(session.updatedAt),
       _meta: toAcpSessionLineageMeta(session),
     };
   }