diff --git a/CHANGELOG.md b/CHANGELOG.md
index c076d705..54725bd3 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]
 
+### Changed
+
+- Setting of `contentType` to use detection when content type is not provided
+
 ## [16.0.0] - 2024-09-25
 
 ### Added
diff --git a/package-lock.json b/package-lock.json
index 6df0c89b..2159e5e6 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -16,6 +16,7 @@
         "@sentry/tracing": "^7.77.0",
         "date-fns": "^2.30.0",
         "file-saver": "^2.0.5",
+        "file-type-checker": "^1.1.2",
         "jwt-decode": "^4.0.0",
         "localforage": "^1.10.0",
         "lodash.clonedeep": "^4.5.0",
@@ -7226,6 +7227,11 @@
       "resolved": "https://registry.npmjs.org/file-saver/-/file-saver-2.0.5.tgz",
       "integrity": "sha512-P9bmyZ3h/PRG+Nzga+rbdI4OEpNDzAVyy74uVO9ATgzLK6VtAsYybF/+TOCvrc0MO793d6+42lLyZTw7/ArVzA=="
     },
+    "node_modules/file-type-checker": {
+      "version": "1.1.2",
+      "resolved": "https://registry.npmjs.org/file-type-checker/-/file-type-checker-1.1.2.tgz",
+      "integrity": "sha512-HodBNiinBQNHQfXhXzAuHkU2udHF3LFS6PAOEZqxW+BjotZVCaMR7ckpTTnvLi718dbzRavnjRX0kbSb5pJG3g=="
+    },
     "node_modules/fill-range": {
       "version": "7.1.1",
       "resolved": "https://registry.npmjs.org/fill-range/-/fill-range-7.1.1.tgz",
@@ -18390,6 +18396,11 @@
       "resolved": "https://registry.npmjs.org/file-saver/-/file-saver-2.0.5.tgz",
       "integrity": "sha512-P9bmyZ3h/PRG+Nzga+rbdI4OEpNDzAVyy74uVO9ATgzLK6VtAsYybF/+TOCvrc0MO793d6+42lLyZTw7/ArVzA=="
     },
+    "file-type-checker": {
+      "version": "1.1.2",
+      "resolved": "https://registry.npmjs.org/file-type-checker/-/file-type-checker-1.1.2.tgz",
+      "integrity": "sha512-HodBNiinBQNHQfXhXzAuHkU2udHF3LFS6PAOEZqxW+BjotZVCaMR7ckpTTnvLi718dbzRavnjRX0kbSb5pJG3g=="
+    },
     "fill-range": {
       "version": "7.1.1",
       "resolved": "https://registry.npmjs.org/fill-range/-/fill-range-7.1.1.tgz",
diff --git a/package.json b/package.json
index f46bb3f9..1ce03fe5 100644
--- a/package.json
+++ b/package.json
@@ -14,6 +14,7 @@
     "@sentry/tracing": "^7.77.0",
     "date-fns": "^2.30.0",
     "file-saver": "^2.0.5",
+    "file-type-checker": "^1.1.2",
     "jwt-decode": "^4.0.0",
     "localforage": "^1.10.0",
     "lodash.clonedeep": "^4.5.0",
diff --git a/src/approvals-service.ts b/src/approvals-service.ts
index 1e906db7..5cbd7207 100644
--- a/src/approvals-service.ts
+++ b/src/approvals-service.ts
@@ -17,7 +17,9 @@ export type FormSubmissionApprovalsResponse = {
     formSubmissionApproval: ApprovalTypes.FormSubmissionApproval
     formApprovalFlowInstance: ApprovalTypes.FormApprovalFlowInstance
     formSubmissionMeta: SubmissionTypes.FormSubmissionMeta
-    latestSuccessfulFormSubmissionPayment: SubmissionTypes.FormSubmissionPayment | undefined
+    latestSuccessfulFormSubmissionPayment:
+      | SubmissionTypes.FormSubmissionPayment
+      | undefined
   }>
 }
 
diff --git a/src/services/uploadAttachment.ts b/src/services/uploadAttachment.ts
index 81e64b62..c1f06d6e 100644
--- a/src/services/uploadAttachment.ts
+++ b/src/services/uploadAttachment.ts
@@ -1,6 +1,7 @@
 import { SubmissionTypes } from '@oneblink/types'
 import { ProgressListener } from '../types/submissions'
 import generateOneBlinkUploader from './generateOneBlinkUploader'
+import fileTypeChecker from 'file-type-checker'
 
 export type UploadAttachmentConfiguration = {
   fileName: string
@@ -64,8 +65,15 @@ export default async function uploadAttachment(
   abortSignal?: AbortSignal,
 ): Promise<SubmissionTypes.FormSubmissionAttachment> {
   const oneblinkUploader = generateOneBlinkUploader()
-  // S3 defaults unknown file types to the following, do the same here for our submission model
-  const _contentType = contentType || 'application/octet-stream'
+
+  let _contentType = contentType || 'application/octet-stream' // S3 default for unknown content type
+  if (!contentType) {
+    const buffer = await data.arrayBuffer()
+    const detectedType = fileTypeChecker.detectFile(buffer)
+    if (detectedType) {
+      _contentType = detectedType.mimeType
+    }
+  }
   const result = await oneblinkUploader.uploadAttachment({
     formId,
     fileName,