diff --git a/app/assets/javascripts/registerSecurityKey.js b/app/assets/javascripts/registerSecurityKey.js
index 993e325e7..69c2c0383 100644
--- a/app/assets/javascripts/registerSecurityKey.js
+++ b/app/assets/javascripts/registerSecurityKey.js
@@ -7,7 +7,10 @@
         .on('click', function(event) {
           event.preventDefault();
 
-          fetchWebAuthnCreateOptions()
+          fetch('/webauthn/register')
+            .then((response) => {
+              return response.arrayBuffer();
+            })
             .then((data) => {
               var options = window.CBOR.decode(data);
               // triggers browser dialogue to select authenticator
@@ -22,45 +25,21 @@
               window.location.reload();
             })
             .catch((error) => {
-              // there may be other kinds of error we should catch here
-              // https://github.com/w3c/webauthn/issues/876
-              if (error instanceof DOMException) {
-                console.error(error);
-                // not all browsers show an error dialogue, so to be safe
-                // we manually pop one open here (to be improved in future!)
-                alert('Error communicating with device.\n\n' + error.message);
-              } else {
-                // for web requests we need to manually alert the user
-                // $.ajax seems to log by itself, but that's not visible
-                alert('Error during registration. Please try again.');
-              }
+              console.error(error);
+              // some browsers will show an error dialogue for some
+              // errors; to be safe we always pop up an alert
+              var message = error.message || error;
+              alert('Error during registration.\n\n' + message);
             });
         });
     };
   };
 
-  function fetchWebAuthnCreateOptions() {
-    var xhrOverride = new XMLHttpRequest();
-    xhrOverride.responseType = 'arraybuffer';
-
-    return $.ajax({
-      url: '/webauthn/register',
-      xhr: () => xhrOverride,
-      dataType: 'x-binary',
-      converters: { '* x-binary': (value) => value }
-    });
-  }
-
   function postWebAuthnCreateResponse(response, csrf_token) {
-    return $.ajax({
-      url: '/webauthn/register',
+    return fetch('/webauthn/register', {
       method: 'POST',
-      headers: {
-        'X-CSRFToken': csrf_token
-      },
-      processData: false,
-      contentType: 'application/cbor',
-      data: window.CBOR.encode({
+      headers: { 'X-CSRFToken': csrf_token },
+      body: window.CBOR.encode({
         attestationObject: new Uint8Array(response.attestationObject),
         clientDataJSON: new Uint8Array(response.clientDataJSON),
       })
diff --git a/tests/javascripts/registerSecurityKey.test.js b/tests/javascripts/registerSecurityKey.test.js
index 3d265fe6f..03b675e1d 100644
--- a/tests/javascripts/registerSecurityKey.test.js
+++ b/tests/javascripts/registerSecurityKey.test.js
@@ -5,10 +5,16 @@ beforeAll(() => {
   // disable console.error() so we don't see it in test output
   // you might need to comment this out to debug some failures
   jest.spyOn(console, 'error').mockImplementation(() => {})
+
+  // populate missing values to allow consistent jest.spyOn()
+  window.fetch = () => {}
 })
 
 afterAll(() => {
   require('./support/teardown.js')
+
+  // restore window attributes to their original undefined state
+  delete window.fetch
 })
 
 describe('Register security key', () => {
@@ -55,16 +61,19 @@ describe('Register security key', () => {
       writable: true,
     })
 
-    jest.spyOn(window.$, 'ajax').mockImplementation((options) => {
+    jest.spyOn(window, 'fetch').mockImplementation((_url, options = {}) => {
       // initial fetch of options from the server
       if (!options.method) {
         // options from the server are CBOR-encoded
         webauthnOptions = window.CBOR.encode('options')
-        return Promise.resolve(webauthnOptions)
+
+        return Promise.resolve({
+          ok: true, arrayBuffer: () => webauthnOptions
+        })
 
       // subsequent POST of credential data to server
       } else {
-        decodedData = window.CBOR.decode(options.data)
+        decodedData = window.CBOR.decode(options.body)
         expect(decodedData.clientDataJSON).toEqual(new Uint8Array([4,5,6]))
         expect(decodedData.attestationObject).toEqual(new Uint8Array([1,2,3]))
         expect(options.headers['X-CSRFToken']).toBe()
@@ -76,13 +85,13 @@ describe('Register security key', () => {
   })
 
   test('alerts if fetching WebAuthn options fails', (done) => {
-    jest.spyOn(window.$, 'ajax').mockImplementation((options) => {
+    jest.spyOn(window, 'fetch').mockImplementation((_url, options = {}) => {
       return Promise.reject('error')
     })
 
     jest.spyOn(window, 'alert').mockImplementation((msg) => {
+      expect(msg).toEqual('Error during registration.\n\nerror')
       done()
-      expect(msg).toEqual('Error during registration. Please try again.')
     })
 
     button.click()
@@ -100,11 +109,14 @@ describe('Register security key', () => {
       writable: true,
     })
 
-    jest.spyOn(window.$, 'ajax').mockImplementation((options) => {
+    jest.spyOn(window, 'fetch').mockImplementation((_url, options = {}) => {
       // initial fetch of options from the server
       if (!options.method) {
         webauthnOptions = window.CBOR.encode('options')
-        return Promise.resolve(webauthnOptions)
+
+        return Promise.resolve({
+          ok: true, arrayBuffer: () => webauthnOptions
+        })
 
       // subsequent POST of credential data to server
       } else {
@@ -113,8 +125,8 @@ describe('Register security key', () => {
     })
 
     jest.spyOn(window, 'alert').mockImplementation((msg) => {
+      expect(msg).toEqual('Error during registration.\n\nerror')
       done()
-      expect(msg).toEqual('Error during registration. Please try again.')
     })
 
     button.click()
@@ -131,15 +143,18 @@ describe('Register security key', () => {
       writable: true,
     })
 
-    jest.spyOn(window.$, 'ajax').mockImplementation((options) => {
+    jest.spyOn(window, 'fetch').mockImplementation((_url, options) => {
       // initial fetch of options from the server
       webauthnOptions = window.CBOR.encode('options')
-      return Promise.resolve(webauthnOptions)
+
+      return Promise.resolve({
+        ok: true, arrayBuffer: () => webauthnOptions
+      })
     })
 
     jest.spyOn(window, 'alert').mockImplementation((msg) => {
+      expect(msg).toEqual('Error during registration.\n\nerror')
       done()
-      expect(msg).toEqual('Error communicating with device.\n\nerror')
     })
 
     button.click()