diff --git a/incorporealcms/__init__.py b/incorporealcms/__init__.py
index 6d87421..8e314b9 100644
--- a/incorporealcms/__init__.py
+++ b/incorporealcms/__init__.py
@@ -40,8 +40,9 @@ def create_app(instance_path=None, test_config=None):
         logger.info("RESPONSE: %s %s: %s", request.method, request.path, response.status)
         return response
 
-    from . import error_pages, pages
+    from . import error_pages, pages, static
     app.register_blueprint(pages.bp)
+    app.register_blueprint(static.bp)
     app.register_error_handler(400, error_pages.bad_request)
     app.register_error_handler(404, error_pages.page_not_found)
     app.register_error_handler(500, error_pages.internal_server_error)
diff --git a/incorporealcms/static.py b/incorporealcms/static.py
new file mode 100644
index 0000000..f7fa083
--- /dev/null
+++ b/incorporealcms/static.py
@@ -0,0 +1,14 @@
+"""Serve static files from the instance directory."""
+import os
+
+from flask import Blueprint
+from flask import current_app as app
+from flask import send_from_directory
+
+bp = Blueprint('static', __name__, url_prefix='/custom-static')
+
+
+@bp.route('/<path:name>')
+def serve_instance_static_file(name):
+    """Serve a static file from the instance directory, used for customization."""
+    return send_from_directory(os.path.join(app.instance_path, 'custom-static'), name)
diff --git a/tests/functional_tests.py b/tests/functional_tests.py
index eb7fb18..9cbb751 100644
--- a/tests/functional_tests.py
+++ b/tests/functional_tests.py
@@ -218,3 +218,23 @@ def test_extra_footer_per_page(client):
     assert b'<div class="extra-footer">' not in response.data
     response = client.get('/index-but-with-footer')
     assert b'<div class="extra-footer"><i>ooo <a href="a">a</a></i>' in response.data
+
+
+def test_serving_static_files(client):
+    """Test the usage of send_from_directory to serve extra static files."""
+    response = client.get('/custom-static/css/warm.css')
+    assert response.status_code == 200
+
+    # can't serve directories, just files
+    response = client.get('/custom-static/')
+    assert response.status_code == 404
+    response = client.get('/custom-static/css/')
+    assert response.status_code == 404
+    response = client.get('/custom-static/css')
+    assert response.status_code == 404
+
+    # can't serve files that don't exist or bad paths
+    response = client.get('/custom-static/css/cold.css')
+    assert response.status_code == 404
+    response = client.get('/custom-static/css/../../unreachable.md')
+    assert response.status_code == 404
diff --git a/tests/instance/custom-static/css/warm.css b/tests/instance/custom-static/css/warm.css
new file mode 100644
index 0000000..0404877
--- /dev/null
+++ b/tests/instance/custom-static/css/warm.css
@@ -0,0 +1,3 @@
+* {
+    color: red;
+}