diff --git a/CHANGELOG.md b/CHANGELOG.md
index e124d61..58a2479 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ## [Unreleased]
 
+### Added
+
+- `username` prop to `uploadPrefillData`
+
 ## [6.0.0] - 2026-03-31
 
 ### Added
diff --git a/src/OneBlinkUploader.ts b/src/OneBlinkUploader.ts
index 0ae932e..62230ef 100644
--- a/src/OneBlinkUploader.ts
+++ b/src/OneBlinkUploader.ts
@@ -435,6 +435,7 @@ export default class OneBlinkUploader {
   async uploadPrefillData({
     formId,
     prefillData,
+    username,
     onProgress,
     abortSignal,
   }: UploadOptions & {
@@ -442,6 +443,8 @@ export default class OneBlinkUploader {
     formId: number
     /** The prefill data to upload */
     prefillData: SubmissionTypes.NewS3SubmissionData['submission']
+    /** A username to allow a single user to download the prefill data */
+    username?: string
   }) {
     return await uploadToS3<{
       preFillFormDataId: string
@@ -452,6 +455,9 @@ export default class OneBlinkUploader {
       key: `forms/${formId}/pre-fill`,
       abortSignal,
       onProgress,
+      requestBodyHeader: {
+        username: username ? encodeURIComponent(username) : undefined,
+      },
     })
   }