diff --git a/src/index.js b/src/index.js
index c7e8f3b..e5aa97c 100644
--- a/src/index.js
+++ b/src/index.js
@@ -314,8 +314,10 @@ async function send(control, action = '', method = 'GET', body = null, enctype =
     if (method === 'GET') {
       action.search = formDataToParams(body).toString()
       body = null
-    } else if (enctype !== 'multipart/form-data') {
+    } else if (enctype !== 'multipart/form-data' && (body instanceof FormData)) {
       body = formDataToParams(body)
+    } else {
+      enctype = null
     }
   }
 
@@ -331,6 +333,8 @@ async function send(control, action = '', method = 'GET', body = null, enctype =
     }, settings.headers, control.headers),
   }
 
+  if (!request.enctype) { delete request.enctype } // Let browser set the correct multipart boundary
+  
   dispatch(control.el, 'ajax:send', request)
 
   let pending
@@ -465,6 +469,13 @@ async function send(control, action = '', method = 'GET', body = null, enctype =
 function parseFormData(data) {
   if (data instanceof FormData) return data
   if (data instanceof HTMLFormElement) return new FormData(data)
+  if (typeof data === 'string') return data
+  if (data instanceof ArrayBuffer) return data
+  if (data instanceof DataView) return data
+  if (data instanceof Blob) return data
+  if (data instanceof File) return data
+  if (data instanceof URLSearchParams) return data
+  if (data instanceof ReadableStream) return data
 
   const formData = new FormData()
   for (let key in data) {
diff --git a/tests/ajax.cy.js b/tests/ajax.cy.js
index f380130..0776899 100644
--- a/tests/ajax.cy.js
+++ b/tests/ajax.cy.js
@@ -53,3 +53,65 @@ test('follows redirects by default',
     })
   }
 )
+
+test('can upload files with $ajax method',
+  html`<button type="button" id="replace" x-init @click="
+    const file = new File(['test content'], 'test.txt', { type: 'text/plain' });
+    $ajax('/tests', {
+      method: 'POST',
+      body: file
+    })
+  "></button>`,
+  ({ intercept, get, wait }) => {
+    intercept('POST', '/tests', {
+      statusCode: 200,
+      body: '<h1 id="title">Success</h1><div id="replace">File uploaded</div>'
+    }).as('response')
+    get('button').click()
+    wait('@response').then((interception) => {
+      // Verify the request body is a File
+      expect(interception.request.body).to.be.equal('test content')
+    })
+})
+
+test('can upload string with $ajax method',
+  html`<button type="button" id="replace" x-init @click="
+    const text = 'test content';
+    $ajax('/tests', {
+      method: 'POST',
+      body: text
+    })
+  "></button>`,
+  ({ intercept, get, wait }) => {
+    intercept('POST', '/tests', {
+      statusCode: 200,
+      body: '<h1 id="title">Success</h1><div id="replace">File uploaded</div>'
+    }).as('response')
+    get('button').click()
+    wait('@response').then((interception) => {
+      // Verify the request body is a File
+      expect(interception.request.body).to.be.equal('test content')
+    })
+})
+
+test('can transform object to FormData with $ajax method',
+  html`<button type="button" id="replace" x-init @click="
+    const obj = { key: 'value', arr: [1,2], nested: { a: 'b' } };
+    $ajax('/tests', {
+      method: 'POST',
+      body: obj
+    })
+  "></button>`,
+  ({ intercept, get, wait }) => {
+    intercept('POST', '/tests', {
+      statusCode: 200,
+      body: '<h1 id="title">Success</h1><div id="replace">File uploaded</div>'
+    }).as('response')
+    get('button').click()
+    wait('@response').then((interception) => {
+      // Verify the request body is a FormData with the correct entries
+      expect(interception.request.body).to.include('key=value')
+      expect(interception.request.body).to.include('arr='+encodeURIComponent(JSON.stringify([1,2]))) // arr=[1,2]
+      expect(interception.request.body).to.include('nested='+encodeURIComponent(JSON.stringify({ a: 'b' }))) // nested={"a":"b"}
+    })
+})