diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 2bc27e3..ef0059d 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -8,7 +8,7 @@ jobs:
 
     strategy:
       matrix:
-        php: [5.3, 5.4, 5.5, 5.6, '7.0', 7.1, 7.2, 7.3, 7.4, '8.0', 8.1, 8.2]
+        php: [5.3, 5.4, 5.5, 5.6, '7.0', 7.1, 7.2, 7.3, 7.4, '8.0', 8.1, 8.2, 8.3]
         flags: ['']
         include:
           - { php: 5.3, flags: --prefer-lowest }
diff --git a/README.md b/README.md
index 5173009..7214d0d 100644
--- a/README.md
+++ b/README.md
@@ -6,7 +6,7 @@ Fixes `assertSame()`/`assertEquals()` serialization errors running in separate p
 
 - php: `>=5.3.3`
 - [phpunit/phpunit](https://github.com/sebastianbergmann/phpunit): `>=4.8.0`
-- [sebastianbergmann/comparator](https://github.com/sebastianbergmann/comparator): `^1.0 || ^2.0 || ^3.0 || ^4.0`
+- [sebastianbergmann/comparator](https://github.com/sebastianbergmann/comparator): `^1.0 || ^2.0 || ^3.0 || ^4.0 || ^5.0 || ^6.0`
 
 ## Installing
 
diff --git a/composer.json b/composer.json
index a2023be..f08a645 100644
--- a/composer.json
+++ b/composer.json
@@ -25,7 +25,7 @@
     },
     "require": {
         "php": ">=5.3.3",
-        "sebastian/comparator": "^1.0 || ^2.0 || ^3.0 || ^4.0"
+        "sebastian/comparator": "^1.0 || ^2.0 || ^3.0 || ^4.0 || ^5.0 || ^6.0"
     },
     "require-dev": {
         "phpunit/phpunit": ">=4.8"