diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index 531745f..f1ea4e2 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -9,7 +9,7 @@ jobs:
         runs-on: ubuntu-latest
         strategy:
             matrix:
-                php-version: ['7.2', '7.3', '7.4', '8.0']
+                php-version: ['7.2', '7.3', '7.4', '8.0', '8.1']
                 composer-flag:
                     - '--prefer-dist'
                     - '--prefer-stable --prefer-lowest'
@@ -38,9 +38,15 @@ jobs:
                   key: ${{ runner.os }}-php-${{ hashFiles('**/composer.lock') }}
                   restore-keys: |
                       ${{ runner.os }}-php-
+
             - name: Install Composer dependencies
               run: composer update ${{ matrix.composer-flag }} --no-interaction --no-progress
 
+            # This may be necessary for older dev packages that do not have
+            #   upper PHP compatibility version constraints.
+            - name: Update Composer Dev dependencies
+              run: composer update phpunit/phpunit --prefer-dist --no-interaction --no-progress
+
             - name: Run Code Style Check for PHP ${{ matrix.php-version }}
               run: composer run-script style-check
 
diff --git a/Dockerfile b/Dockerfile
index d489afc..dd81784 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,4 +1,4 @@
-FROM php:8.0-cli
+FROM php:8.1-cli
 
 # system dependecies
 RUN apt-get update && apt-get install -y \
diff --git a/composer.json b/composer.json
index 1e85a45..062abad 100644
--- a/composer.json
+++ b/composer.json
@@ -12,13 +12,13 @@
     }
   ],
   "require": {
-    "php" : "7.2 - 8.0",
+    "php" : "7.2 - 8.1",
     "ext-json": "*"
   },
   "require-dev": {
     "phpunit/phpunit" : ">=8.2",
     "php-coveralls/php-coveralls": "^2.4",
-    "friendsofphp/php-cs-fixer": "^3.0"
+    "friendsofphp/php-cs-fixer": "^3.4"
   },
   "autoload": {
     "psr-4": {