diff --git a/src/core.ts b/src/core.ts
index 59ea04d6..e016ae54 100644
--- a/src/core.ts
+++ b/src/core.ts
@@ -337,9 +337,13 @@ export abstract class APIClient {
       delete reqHeaders['content-type'];
     }
 
-    // Don't set the retry count header if it was already set or removed by the caller. We check `headers`,
-    // which can contain nulls, instead of `reqHeaders` to account for the removal case.
-    if (getHeader(headers, 'x-stainless-retry-count') === undefined) {
+    // Don't set the retry count header if it was already set or removed through default headers or by the
+    // caller. We check `defaultHeaders` and `headers`, which can contain nulls, instead of `reqHeaders` to
+    // account for the removal case.
+    if (
+      getHeader(defaultHeaders, 'x-stainless-retry-count') === undefined &&
+      getHeader(headers, 'x-stainless-retry-count') === undefined
+    ) {
       reqHeaders['x-stainless-retry-count'] = String(retryCount);
     }
 
diff --git a/tests/index.test.ts b/tests/index.test.ts
index 1b793d88..ab42fae9 100644
--- a/tests/index.test.ts
+++ b/tests/index.test.ts
@@ -332,6 +332,40 @@ describe('retries', () => {
     expect(capturedRequest!.headers as Headers).not.toHaveProperty('x-stainless-retry-count');
   });
 
+  test('omit retry count header by default', async () => {
+    let count = 0;
+    let capturedRequest: RequestInit | undefined;
+    const testFetch = async (url: RequestInfo, init: RequestInit = {}): Promise<Response> => {
+      count++;
+      if (count <= 2) {
+        return new Response(undefined, {
+          status: 429,
+          headers: {
+            'Retry-After': '0.1',
+          },
+        });
+      }
+      capturedRequest = init;
+      return new Response(JSON.stringify({ a: 1 }), { headers: { 'Content-Type': 'application/json' } });
+    };
+    const client = new Mux({
+      tokenId: 'my token id',
+      tokenSecret: 'my secret',
+      fetch: testFetch,
+      maxRetries: 4,
+      defaultHeaders: { 'X-Stainless-Retry-Count': null },
+    });
+
+    expect(
+      await client.request({
+        path: '/foo',
+        method: 'get',
+      }),
+    ).toEqual({ a: 1 });
+
+    expect(capturedRequest!.headers as Headers).not.toHaveProperty('x-stainless-retry-count');
+  });
+
   test('overwrite retry count header', async () => {
     let count = 0;
     let capturedRequest: RequestInit | undefined;