diff --git a/extensions/browser/src/browser/client-fetch.loopback-auth.test.ts b/extensions/browser/src/browser/client-fetch.loopback-auth.test.ts
index e207e60924ce..6d7bb87b2002 100644
--- a/extensions/browser/src/browser/client-fetch.loopback-auth.test.ts
+++ b/extensions/browser/src/browser/client-fetch.loopback-auth.test.ts
@@ -543,6 +543,23 @@ describe("fetchBrowserJson loopback auth", () => {
     );
   });
 
+  it("uses the default timeout for non-finite absolute HTTP timeout failures", async () => {
+    vi.stubGlobal(
+      "fetch",
+      vi.fn(async () => {
+        throw new Error("timed out");
+      }),
+    );
+
+    await expectThrownBrowserFetchError(
+      () => fetchBrowserJson<{ ok: boolean }>("http://example.com/", { timeoutMs: Number.NaN }),
+      {
+        contains: ["timed out after 5000ms"],
+        omits: ["NaNms", "Do NOT retry the browser tool"],
+      },
+    );
+  });
+
   it("omits no-retry hint for absolute HTTP abort failures", async () => {
     vi.stubGlobal(
       "fetch",
diff --git a/extensions/browser/src/browser/client-fetch.ts b/extensions/browser/src/browser/client-fetch.ts
index d65a14e927c2..a9bed1c0d03f 100644
--- a/extensions/browser/src/browser/client-fetch.ts
+++ b/extensions/browser/src/browser/client-fetch.ts
@@ -1,3 +1,4 @@
+import { parseFiniteNumber } from "openclaw/plugin-sdk/number-runtime";
 import { fetchWithSsrFGuard } from "openclaw/plugin-sdk/ssrf-runtime";
 import { normalizeOptionalString } from "openclaw/plugin-sdk/string-coerce-runtime";
 import { normalizeLowercaseStringOrEmpty } from "openclaw/plugin-sdk/string-coerce-runtime";
@@ -162,6 +163,11 @@ function appendBrowserToolModelHint(message: string): string {
 
 type BrowserFetchFailureKind = "timeout" | "aborted" | "persistent";
 
+function resolveBrowserFetchTimeoutMs(timeoutMs: number | undefined): number {
+  const parsed = parseFiniteNumber(timeoutMs);
+  return Math.max(1, Math.floor(parsed ?? 5000));
+}
+
 function classifyBrowserFetchFailure(err: unknown): BrowserFetchFailureKind {
   const msg = normalizeErrorMessage(err);
   const msgLower = normalizeLowercaseStringOrEmpty(msg);
@@ -228,7 +234,7 @@ async function fetchHttpJson<T>(
   url: string,
   init: RequestInit & { timeoutMs?: number },
 ): Promise<T> {
-  const timeoutMs = init.timeoutMs ?? 5000;
+  const timeoutMs = resolveBrowserFetchTimeoutMs(init.timeoutMs);
   const ctrl = new AbortController();
   const upstreamSignal = init.signal;
   let upstreamAbortListener: (() => void) | undefined;
@@ -278,7 +284,7 @@ export async function fetchBrowserJson<T>(
   url: string,
   init?: RequestInit & { timeoutMs?: number },
 ): Promise<T> {
-  const timeoutMs = init?.timeoutMs ?? 5000;
+  const timeoutMs = resolveBrowserFetchTimeoutMs(init?.timeoutMs);
   let isDispatcherPath = false;
   try {
     if (isAbsoluteHttp(url)) {