diff --git a/src/api/MicroPubApi.js b/src/api/MicroPubApi.js
index 3509f104..425f5a52 100644
--- a/src/api/MicroPubApi.js
+++ b/src/api/MicroPubApi.js
@@ -1,7 +1,8 @@
-import { Alert, Platform } from 'react-native';
+import { Alert } from 'react-native';
 import axios from 'axios';
 import { DOMParser } from "@xmldom/xmldom";
 import App from "./../stores/App";
+import { buildUploadFileName } from "../utils/file_names"
 
 export const FETCH_ERROR = 2
 export const POST_ERROR = 3
@@ -330,13 +331,9 @@ class MicroPubApi {
 
 	async upload_media(service, file, destination) {
 		const data = new FormData()
-		// Get extension from file name, for example: 12345.jpg
-		let extension = file.uri.split('.').pop()
-		if (Platform.OS === "android" && file.name != null && file.name !== "") {
-			extension = file.name.split('.').pop()
-		}
+		const file_name = buildUploadFileName(file, Date.now())
 		data.append("file", {
-			name: `media.${extension.toLowerCase()}`,
+			name: file_name,
 			type: file.type,
 			uri: file.uri,
 		})
diff --git a/src/stores/models/posting/uploadLargeMediaTask.js b/src/stores/models/posting/uploadLargeMediaTask.js
index 58ba8503..625258b9 100644
--- a/src/stores/models/posting/uploadLargeMediaTask.js
+++ b/src/stores/models/posting/uploadLargeMediaTask.js
@@ -2,6 +2,7 @@ import { Platform } from "react-native"
 import RNFS from "react-native-fs"
 import axios from "axios"
 import MicroPubApi, { POST_ERROR, FETCH_ERROR } from "../../../api/MicroPubApi"
+import { buildUploadFileName, inferExtensionFromType, sanitizeFileName } from "../../../utils/file_names"
 
 export const LARGE_UPLOAD_CHUNK_SIZE = 1000 * 1024
 export const LARGE_UPLOAD_MAX_SIZE = 1024 * 1024 * 1024
@@ -10,38 +11,6 @@ export const LARGE_UPLOAD_MAX_ATTEMPTS = 45
 
 const wait = ms => new Promise(resolve => setTimeout(resolve, ms))
 
-export const infer_extension_from_type = (mime = "") => {
-	if (mime.includes("quicktime")) {
-		return ".mov"
-	}
-	if (mime.includes("mp4")) {
-		return ".mp4"
-	}
-	if (mime.includes("m4v")) {
-		return ".m4v"
-	}
-	if (mime.includes("webm")) {
-		return ".webm"
-	}
-	if (mime.includes("ogg")) {
-		return ".ogv"
-	}
-	return ".mp4"
-}
-
-export const build_file_name = (media, fallback_id) => {
-	if (media?.fileName) {
-		return media.fileName
-	}
-	if (media?.filename) {
-		return media.filename
-	}
-	if (media?.name) {
-		return media.name
-	}
-	return `upload-${fallback_id}${infer_extension_from_type(media?.type || "")}`
-}
-
 export const ensure_local_uri_for_upload = async (media, fallback_name) => {
 	const current_uri = media?.cached_uri || media?.cachedUri || media?.uri
 	if (!current_uri) {
@@ -50,8 +19,8 @@ export const ensure_local_uri_for_upload = async (media, fallback_name) => {
 	if (current_uri.startsWith("file://")) {
 		return current_uri
 	}
-	const target_name = fallback_name || `upload-${Date.now()}${infer_extension_from_type(media?.type || "")}`
-	const safe_name = target_name.replace(/[^\w.\-]/g, "_")
+	const target_name = fallback_name || `upload-${Date.now()}${inferExtensionFromType(media?.type || "")}`
+	const safe_name = sanitizeFileName(target_name)
 	const target_path = `${RNFS.CachesDirectoryPath}/${Date.now()}-${safe_name}`
 	let source_path = current_uri
 	try {
@@ -98,7 +67,7 @@ export async function upload_large_media_task({
 
 	const active_cancel_source = cancel_source || create_cancel_source()
 	const file_id = Math.floor(Math.random() * 1000000)
-	const file_name = build_file_name(media, file_id)
+	const file_name = buildUploadFileName(media, file_id)
 	const file_type = media?.type || "video/mp4"
 
 	try {
diff --git a/src/utils/file_names.js b/src/utils/file_names.js
new file mode 100644
index 00000000..9d3fae60
--- /dev/null
+++ b/src/utils/file_names.js
@@ -0,0 +1,51 @@
+export const inferExtensionFromType = (mime = "") => {
+  if (mime.includes("quicktime")) {
+    return ".mov"
+  }
+  if (mime.includes("mp4")) {
+    return ".mp4"
+  }
+  if (mime.includes("m4v")) {
+    return ".m4v"
+  }
+  if (mime.includes("webm")) {
+    return ".webm"
+  }
+  if (mime.includes("ogg")) {
+    return ".ogv"
+  }
+  return ".mp4"
+}
+
+const getExtension = name => {
+  if (!name) {
+    return ""
+  }
+  const parts = name.split(".")
+  if (parts.length < 2) {
+    return ""
+  }
+  const extension = parts.pop()
+  if (!extension) {
+    return ""
+  }
+  return `.${extension}`
+}
+
+export const sanitizeFileName = name => {
+  if (!name) {
+    return ""
+  }
+  return name.trim().replace(/[^\w.\-]/g, "_")
+}
+
+export const buildUploadFileName = (media, fallback_id) => {
+  const candidate_name = media?.fileName || media?.filename || media?.name
+  const safe_candidate = sanitizeFileName(candidate_name)
+  const base_name = safe_candidate || `upload-${fallback_id || Date.now()}`
+  const extension = getExtension(base_name)
+  if (!extension) {
+    return `${base_name}${inferExtensionFromType(media?.type || "")}`
+  }
+  return base_name
+}