diff --git a/CHANGELOG.md b/CHANGELOG.md
index efa9c0a..c014d78 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,12 @@ Updates should follow the [Keep a CHANGELOG](https://keepachangelog.com/) princi
 
 ## [Unreleased][unreleased]
 
+## [0.2.1] - 2022-03-30
+
+### Fixed
+
+- Fixed construction of `trusted_host_patterns` array to support sites defined in the `SITES` constant.
+
 ## [0.2.0] - 2022-03-14
 
 ### Changed
@@ -135,7 +141,8 @@ Updates should follow the [Keep a CHANGELOG](https://keepachangelog.com/) princi
 
 **Initial release!**
 
-[unreleased]: https://github.com/unleashedtech/dotenv-drupal/compare/0.2.0...main
+[unreleased]: https://github.com/unleashedtech/dotenv-drupal/compare/0.2.1...main
+[0.2.1]: https://github.com/unleashedtech/dotenv-drupal/compare/0.2.0...0.2.1
 [0.2.0]: https://github.com/unleashedtech/dotenv-drupal/compare/0.1.17...0.2.0
 [0.1.17]: https://github.com/unleashedtech/dotenv-drupal/compare/0.1.16...0.1.17
 [0.1.16]: https://github.com/unleashedtech/dotenv-drupal/compare/0.1.15...0.1.16
diff --git a/README.md b/README.md
index 33a7ed8..9d7d435 100644
--- a/README.md
+++ b/README.md
@@ -244,12 +244,31 @@ so the shorter DSN can be used.
 Streamlined environment-dependent configuration of _one_ Solr core is supported at this time.
 
 #### TRUSTED_HOST_PATTERNS
-Optional. A CSV list of patterns specifying [trusted hosts](https://www.drupal.org/docs/installing-drupal/trusted-host-settings#s-protecting-in-drupal-8). If this
-variable is not set, this package will populate Drupal's `trusted_host_patterns` array
-based on the value of [DOMAINS](#domains).
+Optional. A CSV list of patterns specifying [trusted hosts](https://www.drupal.org/docs/installing-drupal/trusted-host-settings#s-protecting-in-drupal-8).
 
 Start (`^`) & end (`$`) characters are added to every pattern, by default.
 
+##### Fallback Functionality
+If the `TRUSTED_HOST_PATTERNS` variable is _not_ set, this package will populate
+Drupal's `trusted_host_patterns` array based on the values of [DOMAINS](#domains)
+& [SITES](#sites) variables.
+
+###### Examples
+If you have `DOMAINS` set to `foo.example,bar.example`, the Drupal `trusted_host_patterns`
+settings array would have the following values:
+
+* `^foo\.example$`
+* `^www\.foo\.example$`
+* `^bar\.example$`
+* `^www\.bar\.example$`
+
+If you have `DOMAINS` set to `foo.example` & `SITES` set to `bar,baz,qux`, the
+Drupal `trusted_host_patterns` setting array would have the following values:
+
+* `^bar\.foo\.example$`
+* `^baz\.foo\.example$`
+* `^qux\.foo\.example$`
+
 #### Configuration Conclusion
 With these few Environment Variables, you will be able to configure Drupal in a streamlined
 fashion similar to the way Symfony is configured. Support for many more common Drupal features
diff --git a/src/Dotenv.php b/src/Dotenv.php
index 042f8f4..70b667a 100644
--- a/src/Dotenv.php
+++ b/src/Dotenv.php
@@ -259,6 +259,11 @@ public function setDatabaseName(string $database): void
         $this->databaseName = $database;
     }
 
+    public function isMultiSite(): bool
+    {
+        return count($this->getSites()) > 1;
+    }
+
     public function isMultiSiteDefaultSiteAllowed(): bool
     {
         return $this->isMultiSiteDefaultSiteAllowed;
@@ -287,6 +292,10 @@ public function getSettings(): array
         if (isset($_SERVER['HASH_SALT'])) {
             $settings['hash_salt'] = $_SERVER['HASH_SALT'];
         }
+
+        // Configure trusted host patterns.
+        // @see https://github.com/unleashedtech/dotenv-drupal/blob/main/README.md#trusted_host_patterns
+        $settings['trusted_host_patterns'] = [];
         if (isset($_SERVER['TRUSTED_HOST_PATTERNS'])) {
             foreach (explode(',', $_SERVER['TRUSTED_HOST_PATTERNS']) as $pattern) {
                 $settings['trusted_host_patterns'][] = '^' . $pattern . '$';
@@ -294,7 +303,21 @@ public function getSettings(): array
         }
         else {
             foreach ($this->getDomains() as $domain) {
-                $settings['trusted_host_patterns'][] = '^' . str_replace('.', '\.', $domain) . '$';
+                if (! $this->isMultiSite() || $this->isMultiSiteDefaultSiteAllowed()) {
+                    $settings['trusted_host_patterns'][] = '^' . \str_replace('.', '\.', $domain) . '$';
+                    $settings['trusted_host_patterns'][] = '^www\.' . \str_replace('.', '\.', $domain) . '$';
+                }
+
+                foreach ($this->getSites() as $site) {
+                    if ($site === 'default') {
+                        continue;
+                    }
+
+                    $settings['trusted_host_patterns'][] = \vsprintf('^%s\.%s$', [
+                        $site,
+                        \str_replace('.', '\.', $domain),
+                    ]);
+                }
             }
         }