diff --git a/packages/upload-client/src/blob/add.js b/packages/upload-client/src/blob/add.js
index 6872023ac..87d426d71 100644
--- a/packages/upload-client/src/blob/add.js
+++ b/packages/upload-client/src/blob/add.js
@@ -10,6 +10,7 @@ import retry, { AbortError } from 'p-retry'
 import { servicePrincipal, connection } from '../service.js'
 import { REQUEST_RETRIES } from '../constants.js'
 import { poll } from '../receipts.js'
+import { isCloudflareWorkers } from '../runtime.js'
 
 /**
  * @param {string} url
@@ -228,7 +229,7 @@ export async function add(
         try {
           const res = await fetchWithUploadProgress(address.url, {
             method: 'PUT',
-            mode: 'cors',
+            ...(!isCloudflareWorkers && { mode: 'cors' }),
             body: bytes,
             headers: address.headers,
             signal: options.signal,
diff --git a/packages/upload-client/src/runtime.js b/packages/upload-client/src/runtime.js
new file mode 100644
index 000000000..b67c0fb2e
--- /dev/null
+++ b/packages/upload-client/src/runtime.js
@@ -0,0 +1,4 @@
+/* c8 ignore next 3 */
+export const isCloudflareWorkers =
+  typeof navigator !== 'undefined' &&
+  navigator?.userAgent === 'Cloudflare-Workers'