diff --git a/packages/@uppy/transloadit/src/AssemblyOptions.js b/packages/@uppy/transloadit/src/AssemblyOptions.js
index b557717b59..1fc621166b 100644
--- a/packages/@uppy/transloadit/src/AssemblyOptions.js
+++ b/packages/@uppy/transloadit/src/AssemblyOptions.js
@@ -48,7 +48,7 @@ function dedupe (list) {
   }))
 }
 
-async function getAssemblyOptions (file, options) {
+export async function getAssemblyOptions (file, options) {
   const assemblyOptions = typeof options.assemblyOptions === 'function'
     ? await options.assemblyOptions(file, options)
     : options.assemblyOptions
diff --git a/packages/@uppy/transloadit/src/index.js b/packages/@uppy/transloadit/src/index.js
index 8710a18725..cf366058a5 100644
--- a/packages/@uppy/transloadit/src/index.js
+++ b/packages/@uppy/transloadit/src/index.js
@@ -5,7 +5,7 @@ import BasePlugin from '@uppy/core/lib/BasePlugin.js'
 import Tus from '@uppy/tus'
 import Assembly from './Assembly.js'
 import Client from './Client.js'
-import AssemblyOptions, { validateParams } from './AssemblyOptions.js'
+import AssemblyOptions, { validateParams, getAssemblyOptions } from './AssemblyOptions.js'
 import AssemblyWatcher from './AssemblyWatcher.js'
 
 import locale from './locale.js'
@@ -191,12 +191,8 @@ export default class Transloadit extends BasePlugin {
   #createAssembly (fileIDs, uploadID, options) {
     this.uppy.log('[Transloadit] Create Assembly')
 
-    return this.client.createAssembly({
-      params: options.params,
-      fields: options.fields,
-      expectedFiles: fileIDs.length,
-      signature: options.signature,
-    }).then(async (newAssembly) => {
+    const createAssembly = assemblyOptions => this.client.createAssembly(assemblyOptions)
+    return getAssemblyOptions(fileIDs, options).then(createAssembly).then(async (newAssembly) => {
       const files = this.uppy.getFiles().filter(({ id }) => fileIDs.includes(id))
       if (files.length !== fileIDs.length) {
         if (files.length === 0) {