diff --git a/.github/workflows/static.yml b/.github/workflows/static.yml
index 099eb55e7..fcd505587 100644
--- a/.github/workflows/static.yml
+++ b/.github/workflows/static.yml
@@ -7,7 +7,7 @@ on:
   pull_request:
 
 jobs:
-  phpstan:
+  phpstan-src:
     name: PHPStan src
     runs-on: ubuntu-latest
 
@@ -44,3 +44,16 @@ jobs:
         uses: docker://oskarstark/phpstan-ga
         with:
           args: analyze --no-progress -c phpstan.tests.neon.dist
+
+  php-cs-fixer:
+    name: PHP-CS-Fixer
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v2
+
+      - name: PHP-CS-Fixer
+        uses: docker://oskarstark/php-cs-fixer-ga
+        with:
+          args: --dry-run --diff
diff --git a/.gitignore b/.gitignore
index f97c9fc51..ac24059ae 100644
--- a/.gitignore
+++ b/.gitignore
@@ -2,5 +2,6 @@ vendor/
 composer.lock
 phpunit.xml
 doc/_build/
+.php-cs-fixer.cache
 puli.json
 .puli/
diff --git a/.php-cs-fixer.dist.php b/.php-cs-fixer.dist.php
new file mode 100644
index 000000000..92bc74842
--- /dev/null
+++ b/.php-cs-fixer.dist.php
@@ -0,0 +1,18 @@
+<?php
+
+$finder = PhpCsFixer\Finder::create()
+    ->in(__DIR__.'/src')
+    ->in(__DIR__.'/tests')
+    ->name('*.php')
+;
+
+$config = new PhpCsFixer\Config();
+
+return $config
+    ->setRiskyAllowed(true)
+    ->setRules([
+        '@Symfony' => true,
+        'single_line_throw' => false,
+    ])
+    ->setFinder($finder)
+;
diff --git a/.styleci.yml b/.styleci.yml
deleted file mode 100644
index ba4ba743a..000000000
--- a/.styleci.yml
+++ /dev/null
@@ -1,7 +0,0 @@
-preset: symfony
-
-enabled:
-  - alpha_ordered_imports
-
-disabled:
-  - single_line_throw
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 00dee24cb..4f09c3aa9 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,13 @@ Changelog
 
 See also the [GitHub releases page](https://github.com/FriendsOfSymfony/FOSHttpCache/releases).
 
+2.11.0
+------
+
+### Fastly client
+
+- Marked the `@internal` constants in `FOS\HttpCache\ProxyClient\Fastly` as private
+
 2.10.1
 ------
 
diff --git a/src/CacheInvalidator.php b/src/CacheInvalidator.php
index e47b075a4..898bee5c1 100644
--- a/src/CacheInvalidator.php
+++ b/src/CacheInvalidator.php
@@ -40,27 +40,27 @@ class CacheInvalidator
     /**
      * Value to check support of invalidatePath operation.
      */
-    const PATH = 'path';
+    public const PATH = 'path';
 
     /**
      * Value to check support of refreshPath operation.
      */
-    const REFRESH = 'refresh';
+    public const REFRESH = 'refresh';
 
     /**
      * Value to check support of invalidate and invalidateRegex operations.
      */
-    const INVALIDATE = 'invalidate';
+    public const INVALIDATE = 'invalidate';
 
     /**
      * Value to check support of invalidateTags operation.
      */
-    const TAGS = 'tags';
+    public const TAGS = 'tags';
 
     /**
      * Value to check support of clearCache operation.
      */
-    const CLEAR = 'clear';
+    public const CLEAR = 'clear';
 
     /**
      * @var ProxyClient
diff --git a/src/Events.php b/src/Events.php
index 44e3c0609..f9b564277 100644
--- a/src/Events.php
+++ b/src/Events.php
@@ -16,7 +16,7 @@
  */
 final class Events
 {
-    const PROXY_UNREACHABLE_ERROR = 'fos_http_cache.error.proxy_unreachable';
+    public const PROXY_UNREACHABLE_ERROR = 'fos_http_cache.error.proxy_unreachable';
 
-    const PROXY_RESPONSE_ERROR = 'fos_http_cache.error.response';
+    public const PROXY_RESPONSE_ERROR = 'fos_http_cache.error.response';
 }
diff --git a/src/ProxyClient/Fastly.php b/src/ProxyClient/Fastly.php
index b00c897cb..9c1188a2a 100644
--- a/src/ProxyClient/Fastly.php
+++ b/src/ProxyClient/Fastly.php
@@ -32,24 +32,17 @@
  */
 class Fastly extends HttpProxyClient implements ClearCapable, PurgeCapable, RefreshCapable, TagCapable
 {
-    /**
-     * @internal
-     */
-    const HTTP_METHOD_PURGE = 'PURGE';
+    private const HTTP_METHOD_PURGE = 'PURGE';
 
     /**
-     * @internal
-     *
      * @see https://docs.fastly.com/api/purge#purge_db35b293f8a724717fcf25628d713583 Fastly's limit on batch tag purges.
      */
-    const TAG_BATCH_PURGE_LIMIT = 256;
+    private const TAG_BATCH_PURGE_LIMIT = 256;
 
     /**
-     * @internal
-     *
      * @see https://docs.fastly.com/api/purge Base url endpoint used on anything but url PURGE/GET/HEAD.
      */
-    const API_ENDPOINT = 'https://api.fastly.com';
+    private const API_ENDPOINT = 'https://api.fastly.com';
 
     /**
      * {@inheritdoc}
diff --git a/src/ProxyClient/Invalidation/BanCapable.php b/src/ProxyClient/Invalidation/BanCapable.php
index 3a395d244..f556d27b3 100644
--- a/src/ProxyClient/Invalidation/BanCapable.php
+++ b/src/ProxyClient/Invalidation/BanCapable.php
@@ -19,9 +19,9 @@
  */
 interface BanCapable extends ProxyClient
 {
-    const REGEX_MATCH_ALL = '.*';
+    public const REGEX_MATCH_ALL = '.*';
 
-    const CONTENT_TYPE_ALL = self::REGEX_MATCH_ALL;
+    public const CONTENT_TYPE_ALL = self::REGEX_MATCH_ALL;
 
     /**
      * Ban cached objects matching HTTP headers.
diff --git a/src/ProxyClient/Nginx.php b/src/ProxyClient/Nginx.php
index eb2687333..722fb706a 100644
--- a/src/ProxyClient/Nginx.php
+++ b/src/ProxyClient/Nginx.php
@@ -25,11 +25,11 @@
  */
 class Nginx extends HttpProxyClient implements PurgeCapable, RefreshCapable
 {
-    const HTTP_METHOD_PURGE = 'PURGE';
+    public const HTTP_METHOD_PURGE = 'PURGE';
 
-    const HTTP_METHOD_REFRESH = 'GET';
+    public const HTTP_METHOD_REFRESH = 'GET';
 
-    const HTTP_HEADER_REFRESH = 'X-Refresh';
+    public const HTTP_HEADER_REFRESH = 'X-Refresh';
 
     /**
      * {@inheritdoc}
diff --git a/src/ProxyClient/Symfony.php b/src/ProxyClient/Symfony.php
index 57b90bd49..68ca75def 100644
--- a/src/ProxyClient/Symfony.php
+++ b/src/ProxyClient/Symfony.php
@@ -29,7 +29,7 @@
  */
 class Symfony extends HttpProxyClient implements PurgeCapable, RefreshCapable, TagCapable, ClearCapable
 {
-    const HTTP_METHOD_REFRESH = 'GET';
+    public const HTTP_METHOD_REFRESH = 'GET';
 
     /**
      * {@inheritdoc}
diff --git a/src/ProxyClient/Varnish.php b/src/ProxyClient/Varnish.php
index fe1bc7c59..ffb854f1e 100644
--- a/src/ProxyClient/Varnish.php
+++ b/src/ProxyClient/Varnish.php
@@ -37,23 +37,23 @@
  */
 class Varnish extends HttpProxyClient implements BanCapable, PurgeCapable, RefreshCapable, TagCapable
 {
-    const HTTP_METHOD_BAN = 'BAN';
+    public const HTTP_METHOD_BAN = 'BAN';
 
-    const HTTP_METHOD_PURGE = 'PURGE';
+    public const HTTP_METHOD_PURGE = 'PURGE';
 
-    const HTTP_METHOD_PURGEKEYS = 'PURGEKEYS';
+    public const HTTP_METHOD_PURGEKEYS = 'PURGEKEYS';
 
-    const HTTP_METHOD_REFRESH = 'GET';
+    public const HTTP_METHOD_REFRESH = 'GET';
 
-    const HTTP_HEADER_HOST = 'X-Host';
+    public const HTTP_HEADER_HOST = 'X-Host';
 
-    const HTTP_HEADER_URL = 'X-Url';
+    public const HTTP_HEADER_URL = 'X-Url';
 
-    const HTTP_HEADER_CONTENT_TYPE = 'X-Content-Type';
+    public const HTTP_HEADER_CONTENT_TYPE = 'X-Content-Type';
 
-    const TAG_BAN = 'ban';
+    public const TAG_BAN = 'ban';
 
-    const TAG_XKEY = 'purgekeys';
+    public const TAG_XKEY = 'purgekeys';
 
     /**
      * Default name of the header used to invalidate content with specific tags.
@@ -63,9 +63,9 @@ class Varnish extends HttpProxyClient implements BanCapable, PurgeCapable, Refre
      *
      * @var string
      */
-    const DEFAULT_HTTP_HEADER_CACHE_TAGS = 'X-Cache-Tags';
+    public const DEFAULT_HTTP_HEADER_CACHE_TAGS = 'X-Cache-Tags';
 
-    const DEFAULT_HTTP_HEADER_CACHE_XKEY = 'xkey-softpurge';
+    public const DEFAULT_HTTP_HEADER_CACHE_XKEY = 'xkey-softpurge';
 
     /**
      * {@inheritdoc}
diff --git a/src/SymfonyCache/CustomTtlListener.php b/src/SymfonyCache/CustomTtlListener.php
index 37e0f2ea4..474439923 100644
--- a/src/SymfonyCache/CustomTtlListener.php
+++ b/src/SymfonyCache/CustomTtlListener.php
@@ -35,7 +35,7 @@ class CustomTtlListener implements EventSubscriberInterface
      *
      * @var string
      */
-    const SMAXAGE_BACKUP = 'FOS-Smaxage-Backup';
+    public const SMAXAGE_BACKUP = 'FOS-Smaxage-Backup';
 
     /**
      * @param string $ttlHeader The header that is used to specify the TTL header
diff --git a/src/SymfonyCache/Events.php b/src/SymfonyCache/Events.php
index d2b23338f..cb81d9792 100644
--- a/src/SymfonyCache/Events.php
+++ b/src/SymfonyCache/Events.php
@@ -16,11 +16,11 @@
  */
 final class Events
 {
-    const PRE_HANDLE = 'fos_http_cache.pre_handle';
+    public const PRE_HANDLE = 'fos_http_cache.pre_handle';
 
-    const POST_HANDLE = 'fos_http_cache.post_handle';
+    public const POST_HANDLE = 'fos_http_cache.post_handle';
 
-    const PRE_INVALIDATE = 'fos_http_cache.pre_invalidate';
+    public const PRE_INVALIDATE = 'fos_http_cache.pre_invalidate';
 
-    const PRE_STORE = 'fos_http_cache.pre_store';
+    public const PRE_STORE = 'fos_http_cache.pre_store';
 }
diff --git a/src/SymfonyCache/PurgeListener.php b/src/SymfonyCache/PurgeListener.php
index ddb594f0c..28589ab10 100644
--- a/src/SymfonyCache/PurgeListener.php
+++ b/src/SymfonyCache/PurgeListener.php
@@ -25,9 +25,9 @@
  */
 class PurgeListener extends AccessControlledListener
 {
-    const DEFAULT_PURGE_METHOD = 'PURGE';
+    public const DEFAULT_PURGE_METHOD = 'PURGE';
 
-    const DEFAULT_CLEAR_CACHE_HEADER = 'Clear-Cache';
+    public const DEFAULT_CLEAR_CACHE_HEADER = 'Clear-Cache';
 
     /**
      * The purge method to use.
diff --git a/src/SymfonyCache/PurgeTagsListener.php b/src/SymfonyCache/PurgeTagsListener.php
index eb4d02f20..233c7d351 100644
--- a/src/SymfonyCache/PurgeTagsListener.php
+++ b/src/SymfonyCache/PurgeTagsListener.php
@@ -24,9 +24,9 @@
  */
 class PurgeTagsListener extends AccessControlledListener
 {
-    const DEFAULT_TAGS_METHOD = 'PURGETAGS';
+    public const DEFAULT_TAGS_METHOD = 'PURGETAGS';
 
-    const DEFAULT_TAGS_HEADER = 'X-Cache-Tags';
+    public const DEFAULT_TAGS_HEADER = 'X-Cache-Tags';
 
     /**
      * The purge tags method to use.
diff --git a/src/TagHeaderFormatter/TagHeaderFormatter.php b/src/TagHeaderFormatter/TagHeaderFormatter.php
index 93046e34a..83fe3be00 100644
--- a/src/TagHeaderFormatter/TagHeaderFormatter.php
+++ b/src/TagHeaderFormatter/TagHeaderFormatter.php
@@ -23,7 +23,7 @@ interface TagHeaderFormatter
      *
      * @var string
      */
-    const DEFAULT_HEADER_NAME = 'X-Cache-Tags';
+    public const DEFAULT_HEADER_NAME = 'X-Cache-Tags';
 
     /**
      * Get the HTTP header name that will hold cache tags.