diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 09d73b7..d02fdc8 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -35,7 +35,7 @@ jobs:
       - name: Install dependencies and package
         run: |
           python -m pip install --upgrade pip
-          pip install -r requirements.txt
+          pip install -r requirements-test.txt
           pip install django~=${{ matrix.django-version }}.0
           pip install djangorestframework~=${{ matrix.djangorestframework-version }}.0
 
diff --git a/README.md b/README.md
index a7099b9..4f28890 100644
--- a/README.md
+++ b/README.md
@@ -9,6 +9,12 @@ If used with DRF, `django-filter` is an additional requirement.
 
 1. Install using pip:
 
+```shell
+pip install drf-attachments[drf]
+```
+
+or to install without DRF dependencies (no REST endpoints available from scratch)
+
 ```shell
 pip install drf-attachments
 ```
@@ -140,6 +146,12 @@ def attachment_context_translations():
     }
 ```
 
+4. Optionally define a custom DIR as root for your attachments ("attachments" by default)
+```python
+# settings.py
+ATTACHMENT_UPLOAD_ROOT_DIR = "your/custom/attachments/root/"
+```
+
 ## Usage
 
 Attachments accept any other Model as content_object and store the uploaded files in their respective directories
diff --git a/drf_attachments/models/models.py b/drf_attachments/models/models.py
index 436e915..ececbcd 100644
--- a/drf_attachments/models/models.py
+++ b/drf_attachments/models/models.py
@@ -13,7 +13,7 @@
     UUIDField,
 )
 from django.utils.translation import gettext_lazy as _
-from rest_framework.exceptions import ValidationError
+from django.core.exceptions import ValidationError
 
 from drf_attachments.config import config
 from drf_attachments.models.fields import DynamicStorageFileField
@@ -99,6 +99,16 @@ class Meta:
         verbose_name_plural = _("attachments")
         ordering = ("creation_date",)
 
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        try:
+            # if DRF is installed, use their ValidationError
+            from rest_framework.exceptions import ValidationError as DrfValidationError
+            self.validation_error_class = DrfValidationError
+        except ImportError:
+            # otherwise use default django ValidationError
+            self.validation_error_class = ValidationError
+
     def __str__(self):
         return f"{self.content_type} | {self.object_id} | {self.context_label} | {self.name}"
 
@@ -184,12 +194,7 @@ def validate_context(self):
                 context=self.context,
                 valid_contexts=", ".join(self.valid_contexts),
             )
-            raise ValidationError(
-                {
-                    "context": error_msg,
-                },
-                code="invalid",
-            )
+            raise self.validation_error_class(error_msg, code="invalid")
 
     def validate_file(self):
         """
@@ -214,7 +219,7 @@ def _validate_file_mime_type(self):
                 mime_type=self.meta["mime_type"],
                 valid_mime_types=", ".join(self.valid_mime_types),
             )
-            raise ValidationError(
+            raise self.validation_error_class(
                 {
                     "file": error_msg,
                 },
@@ -236,7 +241,7 @@ def _validate_file_extension(self):
                 extension=self.meta["extension"],
                 valid_extensions=", ".join(self.valid_extensions),
             )
-            raise ValidationError(
+            raise self.validation_error_class(
                 {
                     "file": error_msg,
                 },
@@ -257,7 +262,7 @@ def _validate_file_size(self):
                 size=self.file.size,
                 min_size=self.min_size,
             )
-            raise ValidationError(
+            raise self.validation_error_class(
                 {
                     "file": error_msg,
                 },
@@ -272,7 +277,7 @@ def _validate_file_size(self):
                 size=self.file.size,
                 max_size=self.max_size,
             )
-            raise ValidationError(
+            raise self.validation_error_class(
                 {
                     "file": error_msg,
                 },
diff --git a/drf_attachments/storage.py b/drf_attachments/storage.py
index 43ca370..c68c0e4 100644
--- a/drf_attachments/storage.py
+++ b/drf_attachments/storage.py
@@ -33,6 +33,13 @@ def url(self, name):
         return get_admin_attachment_url(attachment.pk)
 
 
+def attachment_upload_root_dir():
+    """
+    Extract ATTACHMENT_UPLOAD_ROOT_DIR from the settings (if defined)
+    """
+    return getattr(settings, "ATTACHMENT_UPLOAD_ROOT_DIR", "attachments")
+
+
 def attachment_upload_path(attachment, filename):
     """
     If not defined otherwise, a content_object's attachment files will be uploaded as
@@ -47,4 +54,4 @@ def attachment_upload_path(attachment, filename):
     """
     filename, file_extension = os.path.splitext(filename)
     month_directory = timezone.now().strftime("%Y%m")
-    return f"attachments/{month_directory}/{str(uuid1())}{file_extension}"
+    return f"{attachment_upload_root_dir()}/{month_directory}/{str(uuid1())}{file_extension}"
diff --git a/requirements-test.txt b/requirements-test.txt
new file mode 100644
index 0000000..140e8e2
--- /dev/null
+++ b/requirements-test.txt
@@ -0,0 +1,4 @@
+# load base requirements
+-r base.txt
+
+rest-framework-generic-relations>=2.0.0
\ No newline at end of file
diff --git a/requirements.txt b/requirements.txt
index f3d053f..b4bb813 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -15,9 +15,7 @@ black>=22.6.0,<22.7
 
 # TestApp dependencies
 django>=3.2,<4
-djangorestframework>=3.13,<4
 python-magic>=0.4.18
-rest-framework-generic-relations>=2.0.0
 django-filter>=21.1,<22
 
 # fix importlib version to avoid "AttributeError: 'EntryPoints' object has no attribute 'get'" with flake8
diff --git a/setup.py b/setup.py
index c6bb472..42de1e9 100644
--- a/setup.py
+++ b/setup.py
@@ -22,7 +22,6 @@
     author_email="abruckner@anexia-it.com",
     install_requires=[
         "python-magic>=0.4.18",
-        "rest-framework-generic-relations>=2.0.0",
         "content-disposition>=1.1.0",
     ],
     classifiers=[
@@ -39,4 +38,7 @@
         "Programming Language :: Python :: 3.9",
         "Programming Language :: Python :: 3.10",
     ],
+    extras_require={
+        "drf": ["rest-framework-generic-relations>=2.0.0"],
+    },
 )
diff --git a/tests/testapp/tests/test_api.py b/tests/testapp/tests/test_api.py
index 162ef68..e61c25a 100644
--- a/tests/testapp/tests/test_api.py
+++ b/tests/testapp/tests/test_api.py
@@ -98,18 +98,19 @@ def test_download(self):
 
         # get attachment from main serializer
         response = self.client.get(path=f"/api/attachment/")
-        attachment_response = response.json()[0]
-        # TODO: download_url is not provided by main serializer. intentional?
+        main_attachment_response = response.json()[0]
+        main_download_url = main_attachment_response["download_url"]
+        self.assertIsNotNone(main_download_url)
+        self.assertGreater(len(main_download_url), 0)
 
         # get attachment from sub-serializer
         response = self.client.get(path=f"/api/photo_album/{self.photo_album.pk}/")
-        attachment_response = response.json()["attachments"][0]
-        download_url = attachment_response["download_url"]
-        self.assertIsNotNone(download_url)
-        self.assertGreater(len(download_url), 0)
+        sub_attachment_response = response.json()["attachments"][0]
+        sub_download_url = sub_attachment_response["download_url"]
+        self.assertEqual(main_download_url, sub_download_url)
 
         # download
-        response = self.client.get(download_url)
+        response = self.client.get(sub_download_url)
 
         # check response
         self.assertEqual(