diff --git a/.circleci/config.yml b/.circleci/config.yml
index 4badb855..838c713d 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -9,7 +9,7 @@ workflows:
       - test-on-linux:
           matrix:
               parameters:
-                  php-version: ["7.3", "7.4", "8.0"]
+                  php-version: ["7.3", "7.4", "8.0", "8.1"]
                   composer-dependencies: ["lowest", "highest"]
       - test-on-windows
 
@@ -79,9 +79,14 @@ jobs:
       - run:
           name: psalm linting
           command: ./vendor/bin/psalm --no-cache
-      - run:
-          name: php-cs-fixer check
-          command: composer cs-check
+      - when:
+          condition:
+              not:
+                equal: [ "8.1", <<parameters.php-version>> ]
+          steps:
+            - run:
+                name: php-cs-fixer check
+                command: composer cs-check
       - run:
           name: run tests
           command: php -d xdebug.mode=coverage vendor/bin/phpunit
diff --git a/composer.json b/composer.json
index 4da99fc7..d957502d 100644
--- a/composer.json
+++ b/composer.json
@@ -15,16 +15,16 @@
     ],
     "require": {
         "php": ">=7.3",
-        "monolog/monolog": "^1.6|^2.0",
+        "monolog/monolog": "^1.6|^2.0|^3.0",
         "psr/log": "^1.0|^2.0|^3.0"
     },
     "require-dev": {
         "friendsofphp/php-cs-fixer": ">=2.18.0 <3.0",
         "guzzlehttp/guzzle": "^6.3 | ^7",
-        "kevinrob/guzzle-cache-middleware": "^3",
+        "kevinrob/guzzle-cache-middleware": "^4.0",
         "phpunit/php-code-coverage": "^9",
         "phpunit/phpunit": "^9",
-        "vimeo/psalm": "^4.4"
+        "vimeo/psalm": "^4.9"
     },
     "suggest": {
         "guzzlehttp/guzzle": "(^6.3 | ^7) Required when using GuzzleEventPublisher or the default FeatureRequester",
diff --git a/tests/LDClientTest.php b/tests/LDClientTest.php
index 1589e8cc..4679cae5 100644
--- a/tests/LDClientTest.php
+++ b/tests/LDClientTest.php
@@ -711,7 +711,7 @@ public function testSecureModeHash()
 
     public function testLoggerInterfaceWarn()
     {
-        // Use LoggerInterface impl, instead of concreate Logger from Monolog, to demonstrate the problem with `warn`.
+        // Use LoggerInterface impl, instead of concrete Logger from Monolog, to demonstrate the problem with `warn`.
         $logger = $this->getMockBuilder(LoggerInterface::class)->getMock();
 
         $logger->expects(self::atLeastOnce())->method('warning');