diff --git a/src/evaluate.test.ts b/src/evaluate.test.ts
index e640e99..6db0e63 100644
--- a/src/evaluate.test.ts
+++ b/src/evaluate.test.ts
@@ -1,4 +1,4 @@
-import { afterEach, beforeEach, describe, expect, test } from "bun:test";
+import { afterEach, beforeEach, describe, expect, spyOn, test } from "bun:test";
 import { createDefaultScheduler } from "@intx/inference";
 
 import type { EvaluateDeps } from "./client";
@@ -168,6 +168,32 @@ describe("evaluate without a transport", () => {
   });
 });
 
+describe("evaluate with the default transport", () => {
+  test("calls the global fetch unbound, as browsers require", async () => {
+    const fetchSpy = spyOn(globalThis, "fetch").mockImplementation(
+      Object.assign(
+        function browserLikeFetch(this: unknown): Promise<Response> {
+          if (this !== undefined && this !== globalThis) {
+            throw new TypeError("Illegal invocation");
+          }
+          return Promise.reject(new TypeError("offline"));
+        },
+        { preconnect: globalThis.fetch.preconnect },
+      ),
+    );
+    try {
+      const result = await evaluate({
+        state: {},
+        questions,
+        config: { apiKey: "key" },
+      });
+      expect(result).toMatchObject({ reason: "network", detail: "offline" });
+    } finally {
+      fetchSpy.mockRestore();
+    }
+  });
+});
+
 // Records the bearer key and timeout of the one POST `evaluate` makes; the
 // POST fails at once, so each call ends in a network fallback.
 function recordingDeps(): {
diff --git a/src/evaluate.ts b/src/evaluate.ts
index 5fcff32..a0c096f 100644
--- a/src/evaluate.ts
+++ b/src/evaluate.ts
@@ -251,7 +251,8 @@ export async function evaluate(
   options?: EvaluateOptions,
 ): Promise<EvaluateResult | FallbackResult> {
   const deps: EvaluateDeps = options?.deps ?? {
-    fetch: globalThis.fetch,
+    // Browsers reject fetch called as a method of another object.
+    fetch: (input, init) => fetch(input, init),
     scheduler: createDefaultScheduler(),
   };
   const start = deps.scheduler.now();