diff --git a/s3file/forms.py b/s3file/forms.py
index e0e9d99..9c29e45 100644
--- a/s3file/forms.py
+++ b/s3file/forms.py
@@ -1,5 +1,6 @@
+import base64
 import logging
-import os
+import pathlib
 import uuid
 
 from django.conf import settings
@@ -13,7 +14,7 @@ class S3FileInputMixin:
     """FileInput that uses JavaScript to directly upload to Amazon S3."""
 
     needs_multipart_form = False
-    upload_path = getattr(settings, 'S3FILE_UPLOAD_PATH', os.path.join('tmp', 's3file'))
+    upload_path = getattr(settings, 'S3FILE_UPLOAD_PATH', pathlib.PurePosixPath('tmp', 's3file'))
     expires = settings.SESSION_COOKIE_AGE
 
     @property
@@ -29,7 +30,7 @@ def build_attrs(self, *args, **kwargs):
 
         accept = attrs.get('accept')
         response = self.client.generate_presigned_post(
-            self.bucket_name, os.path.join(self.upload_folder, '${filename}'),
+            self.bucket_name, str(pathlib.PurePosixPath(self.upload_folder, '${filename}')),
             Conditions=self.get_conditions(accept),
             ExpiresIn=self.expires,
         )
@@ -50,7 +51,7 @@ def build_attrs(self, *args, **kwargs):
     def get_conditions(self, accept):
         conditions = [
             {"bucket": self.bucket_name},
-            ["starts-with", "$key", self.upload_folder],
+            ["starts-with", "$key", str(self.upload_folder)],
             {"success_action_status": "201"},
         ]
         if accept and ',' not in accept:
@@ -66,10 +67,12 @@ def get_conditions(self, accept):
 
     @cached_property
     def upload_folder(self):
-        return os.path.join(
+        return str(pathlib.PurePosixPath(
             self.upload_path,
-            uuid.uuid4().hex,
-        )
+            base64.urlsafe_b64encode(
+                uuid.uuid4().bytes
+            ).decode('utf-8').rstrip('=\n'),
+        ))  # S3 uses POSIX paths
 
     class Media:
         js = (
diff --git a/tests/conftest.py b/tests/conftest.py
index c5fe447..83e6c6a 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -14,7 +14,7 @@ def driver():
     chrome_options.add_argument('headless')
     chrome_options.add_argument('window-size=1200x800')
     try:
-        b = webdriver.Chrome(chrome_options=chrome_options)
+        b = webdriver.Chrome(options=chrome_options)
     except WebDriverException as e:
         pytest.skip(force_text(e))
     else:
diff --git a/tests/test_forms.py b/tests/test_forms.py
index c1b2041..2ad8780 100644
--- a/tests/test_forms.py
+++ b/tests/test_forms.py
@@ -165,3 +165,7 @@ def test_file_insert_submit_value(self, driver, live_server, upload_file, freeze
 
     def test_media(self):
         assert ClearableFileInput().media._js == ['s3file/js/s3file.js']
+
+    def test_upload_folder(self):
+        assert ClearableFileInput().upload_folder.startswith('tmp/s3file/')
+        assert len(ClearableFileInput().upload_folder) == 33
diff --git a/tests/testapp/settings.py b/tests/testapp/settings.py
index 8a17763..4b62f80 100644
--- a/tests/testapp/settings.py
+++ b/tests/testapp/settings.py
@@ -52,3 +52,4 @@
 AWS_STORAGE_BUCKET_NAME = 'test-bucket'
 AWS_S3_REGION_NAME = 'eu-central-1'
 AWS_S3_SIGNATURE_VERSION = 's3v4'
+AWS_DEFAULT_ACL = None