diff --git a/src/client.ts b/src/client.ts
index aa661b2d..5ebf4fd9 100644
--- a/src/client.ts
+++ b/src/client.ts
@@ -1835,6 +1835,32 @@ export class Zernio {
       })
     );
 
+    // `_bind` injects this instance's client under the `client` key so each
+    // operation runs on the right per-instance client. @hey-api/client-fetch
+    // then spreads the whole per-request options object — `client` included —
+    // into the fetch `RequestInit`. Node's undici ignores unknown init fields,
+    // but Deno (and other WinterCG runtimes) reject a `client` that is not a
+    // `Deno.HttpClient`, so `new Request(...)` throws
+    // "Failed to construct 'Request': Argument 2 `client` must be a
+    // Deno.HttpClient" and every call fails under Deno Deploy, Supabase Edge
+    // Functions, Cloudflare Workers, etc. The selector has already done its job
+    // before the HTTP method runs, so strip it before the request is built.
+    const dispatchers = this._client as unknown as Record<
+      string,
+      (requestOptions?: Record<string, unknown>) => unknown
+    >;
+    for (const method of ['get', 'post', 'put', 'patch', 'delete', 'head', 'options', 'trace', 'connect']) {
+      const dispatch = dispatchers[method].bind(this._client);
+      dispatchers[method] = (requestOptions) => {
+        if (requestOptions && 'client' in requestOptions) {
+          const withoutClientSelector = { ...requestOptions };
+          delete withoutClientSelector['client'];
+          return dispatch(withoutClientSelector);
+        }
+        return dispatch(requestOptions);
+      };
+    }
+
     // Add auth interceptor
     this._client.interceptors.request.use((request) => {
       request.headers.set('Authorization', `Bearer ${this.apiKey}`);
diff --git a/tests/request-init.test.ts b/tests/request-init.test.ts
new file mode 100644
index 00000000..40532545
--- /dev/null
+++ b/tests/request-init.test.ts
@@ -0,0 +1,63 @@
+import { describe, it, expect, beforeEach, afterEach, vi } from 'vitest';
+import Zernio from '../src';
+
+/**
+ * `_bind` injects this instance's client under the `client` key so each call
+ * runs on the right per-instance client. @hey-api/client-fetch then spreads the
+ * whole per-request options object into the fetch `RequestInit`. Node's undici
+ * ignores unknown init fields, but Deno (and other WinterCG runtimes) reject a
+ * `client` that is not a `Deno.HttpClient` — `new Request(...)` throws and every
+ * call fails under Deno Deploy, Supabase Edge Functions, Cloudflare Workers.
+ *
+ * This asserts the selector never reaches the RequestInit. It runs under Node,
+ * so it captures the init at `new Request` time (undici would otherwise silently
+ * swallow the stray field and hide the bug).
+ */
+describe('request construction (Deno / WinterCG compatibility)', () => {
+  const OriginalRequest = globalThis.Request;
+  const originalFetch = globalThis.fetch;
+  let capturedInits: (RequestInit | undefined)[];
+
+  beforeEach(() => {
+    capturedInits = [];
+    globalThis.Request = class extends OriginalRequest {
+      constructor(input: RequestInfo | URL, init?: RequestInit) {
+        capturedInits.push(init);
+        super(input, init);
+      }
+    } as unknown as typeof Request;
+    globalThis.fetch = vi.fn(
+      async () =>
+        new Response('{}', { status: 200, headers: { 'content-type': 'application/json' } })
+    ) as unknown as typeof fetch;
+  });
+
+  afterEach(() => {
+    globalThis.Request = OriginalRequest;
+    globalThis.fetch = originalFetch;
+  });
+
+  it('never leaks the internal client into the fetch RequestInit', async () => {
+    const client = new Zernio({ apiKey: 'sk_test' });
+
+    await client.accounts.listAccounts({});
+
+    expect(capturedInits.length).toBeGreaterThan(0);
+    for (const init of capturedInits) {
+      expect(init && 'client' in init).toBe(false);
+    }
+  });
+
+  it('still selects the per-instance client (auth header is applied)', async () => {
+    const authHeaders: (string | null)[] = [];
+    globalThis.fetch = vi.fn(async (input: RequestInfo | URL) => {
+      authHeaders.push((input as Request).headers.get('Authorization'));
+      return new Response('{}', { status: 200, headers: { 'content-type': 'application/json' } });
+    }) as unknown as typeof fetch;
+
+    const client = new Zernio({ apiKey: 'sk_ABCD' });
+    await client.accounts.listAccounts({});
+
+    expect(authHeaders).toEqual(['Bearer sk_ABCD']);
+  });
+});