diff --git a/addons/website/models/website.py b/addons/website/models/website.py
index 42b20802b86..8f680b1a73e 100644
--- a/addons/website/models/website.py
+++ b/addons/website/models/website.py
@@ -930,6 +930,15 @@ class Website(models.Model):
 
     @api.model
     def get_current_website(self, fallback=True):
+        """ The current website is returned in the following order:
+        - the website forced in session `force_website_id`
+        - the website set in context
+        - (if frontend or fallback) the website matching the request's "domain"
+        - arbitrary the first website found in the database if `fallback` is set
+          to `True`
+        - empty browse record
+        """
+        is_frontend_request = request and getattr(request, 'is_frontend', False)
         if request and request.session.get('force_website_id'):
             website_id = self.browse(request.session['force_website_id']).exists()
             if not website_id:
@@ -942,12 +951,22 @@ class Website(models.Model):
         if website_id:
             return self.browse(website_id)
 
-        if not request and not fallback:
+        if not is_frontend_request and not fallback:
+            # It's important than backend requests with no fallback requested
+            # don't go through
             return self.browse(False)
 
+        # Reaching this point means that:
+        # - We didn't find a website in the session or in the context.
+        # - And we are either:
+        #   - in a frontend context
+        #   - in a backend context (or early in the dispatch stack) and a
+        #     fallback website is requested.
+        # We will now try to find a website matching the request host/domain (if
+        # there is one on request) or return a random one.
+
         # The format of `httprequest.host` is `domain:port`
         domain_name = request and request.httprequest.host or ''
-
         website_id = self._get_current_website_id(domain_name, fallback=fallback)
         return self.browse(website_id)
 
diff --git a/addons/website/tests/__init__.py b/addons/website/tests/__init__.py
index 63fccfa6a24..b44bdd38129 100644
--- a/addons/website/tests/__init__.py
+++ b/addons/website/tests/__init__.py
@@ -1,5 +1,6 @@
 # -*- coding: utf-8 -*-
 # Part of Odoo. See LICENSE file for full copyright and licensing details.
+from . import test_assets
 from . import test_attachment
 from . import test_auth_signup_uninvited
 from . import test_automatic_editor
diff --git a/addons/website/tests/test_assets.py b/addons/website/tests/test_assets.py
new file mode 100644
index 00000000000..5dbacafa878
--- /dev/null
+++ b/addons/website/tests/test_assets.py
@@ -0,0 +1,65 @@
+# -*- coding: utf-8 -*-
+# Part of Odoo. See LICENSE file for full copyright and licensing details.
+
+import odoo.tests
+
+from odoo.tools import config
+
+
+@odoo.tests.common.tagged('post_install', '-at_install')
+class TestWebsiteAssets(odoo.tests.HttpCase):
+
+    def test_01_multi_domain_assets_generation(self):
+        Website = self.env['website']
+        Attachment = self.env['ir.attachment']
+        # Simulate single website DBs: make sure other website do not interfer
+        # (We can't delete those, constraint will most likely be raised)
+        Website.search([]).write({'domain': 'inactive.test'})
+        # Don't use HOST, hardcode it so it doesn't get changed one day and make
+        # the test useless
+        domain_1 = "http://127.0.0.1:%s" % config['http_port']
+        domain_2 = "http://localhost:%s" % config['http_port']
+        Website.browse(1).domain = domain_1
+
+        self.authenticate('admin', 'admin')
+        self.env['web_editor.assets'].with_context(website_id=1).make_scss_customization(
+            '/website/static/src/scss/options/colors/user_color_palette.scss',
+            {"o-cc1-bg": "'400'"},
+        )
+
+        def get_last_backend_asset_attach_id():
+            return Attachment.search([
+                ('name', '=', 'web.assets_backend.min.js'),
+            ], order="id desc", limit=1).id
+
+        def check_asset():
+            self.assertEqual(last_backend_asset_attach_id, get_last_backend_asset_attach_id())
+
+        last_backend_asset_attach_id = get_last_backend_asset_attach_id()
+
+        # The first call will generate the assets and populate the cache and
+        # take ~100 SQL Queries (~cold state).
+        # Any later call to `/web`, regardless of the domain, will take only
+        # ~10 SQL Queries (hot state).
+        # Without the calls the `check_asset()` (which would raise early and
+        # would not call other `url_open()`) and before the fix coming with this
+        # test, here is the logs:
+        #      "GET /web HTTP/1.1" 200 - 222 0.135 3.840  <-- 222 Queries, ~4s
+        #      "GET /web HTTP/1.1" 200 - 181 0.101 3.692  <-- 181 Queries, ~4s
+        #      "GET /web HTTP/1.1" 200 - 215 0.121 3.704  <-- 215 Queries, ~4s
+        #      "GET /web HTTP/1.1" 200 - 181 0.100 3.616  <-- 181 Queries, ~4s
+        # After the fix, here is the logs:
+        #      "GET /web HTTP/1.1" 200 - 101 0.043 0.353  <-- 101 Queries, ~0.3s
+        #      "GET /web HTTP/1.1" 200 - 11 0.004 0.007   <--  11 Queries, ~10ms
+        #      "GET /web HTTP/1.1" 200 - 11 0.003 0.005   <--  11 Queries, ~10ms
+        #      "GET /web HTTP/1.1" 200 - 11 0.003 0.008   <--  11 Queries, ~10ms
+        self.url_open(domain_1 + '/web')
+        check_asset()
+        self.url_open(domain_2 + '/web')
+        check_asset()
+        self.url_open(domain_1 + '/web')
+        check_asset()
+        self.url_open(domain_2 + '/web')
+        check_asset()
+        self.url_open(domain_1 + '/web')
+        check_asset()