diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index a227e3c..9eb6b5a 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -96,10 +96,18 @@ jobs:
             phpunit: '11.0.0'
             coverage: true
             experimental: false
+          - php: '8.3'
+            phpunit: '12.0.0'
+            coverage: true
+            experimental: false
           - php: '8.4'
             phpunit: '11.3.6'
             coverage: true
             experimental: false
+          - php: '8.4'
+            phpunit: '12.0.0'
+            coverage: true
+            experimental: false
 
           # Experimental builds.
           - php: 'nightly'
@@ -107,12 +115,16 @@ jobs:
             coverage: false
             experimental: true
           - php: 'nightly'
-            phpunit: 'auto' # PHPUnit 11.x.
+            phpunit: '^11.5'
+            coverage: false
+            experimental: true
+          - php: 'nightly'
+            phpunit: 'auto' # PHPUnit 12.x.
             coverage: false
             experimental: true
 
           - php: 'latest'
-            phpunit: 'dev-main' # PHPUnit 12.x.
+            phpunit: 'dev-main' # PHPUnit 12.x/13.x.
             coverage: false
             experimental: true
 
@@ -168,6 +180,8 @@ jobs:
         run: |
           if [ "${{ matrix.phpunit == 'dev-main' }}" == "true" ]; then
             echo 'FILE=phpunit10.xml.dist' >> "$GITHUB_OUTPUT"
+          elif [ "${{ startsWith( steps.phpunit_version.outputs.VERSION, '12.' ) }}" == "true" ]; then
+            echo 'FILE=phpunit10.xml.dist' >> "$GITHUB_OUTPUT"
           elif [ "${{ startsWith( steps.phpunit_version.outputs.VERSION, '11.' ) }}" == "true" ]; then
             echo 'FILE=phpunit10.xml.dist' >> "$GITHUB_OUTPUT"
           else
@@ -287,11 +301,25 @@ jobs:
             phpunit: '11'
             coverage: true
 
+          # PHPUnit 12 is fully supported for the officially supported PHP versions.
+          - php: '8.3'
+            phpunit: '12.0'
+          - php: '8.3'
+            phpunit: '12'
+            coverage: true
+          - php: '8.4'
+            phpunit: '12.0'
+          - php: '8.4'
+            phpunit: '12'
+            coverage: true
+
           # Experimental builds.
           - php: 'nightly'
             phpunit: '9'
           - php: 'nightly'
             phpunit: '11'
+          - php: 'nightly'
+            phpunit: '12'
 
     name: "PHAR test: PHP ${{ matrix.php }} - PHPUnit: ${{matrix.phpunit}}"
 
@@ -348,7 +376,9 @@ jobs:
       - name: Determine PHPUnit config
         id: phpunit_config
         run: |
-          if [ "${{ startsWith( steps.phpunit_version.outputs.VERSION, '11.' ) }}" == "true" ]; then
+          if [ "${{ startsWith( steps.phpunit_version.outputs.VERSION, '12.' ) }}" == "true" ]; then
+            echo 'FILE=phpunit10.xml.dist' >> "$GITHUB_OUTPUT"
+          elif [ "${{ startsWith( steps.phpunit_version.outputs.VERSION, '11.' ) }}" == "true" ]; then
             echo 'FILE=phpunit10.xml.dist' >> "$GITHUB_OUTPUT"
           else
             echo 'FILE=phpunit.xml.dist' >> "$GITHUB_OUTPUT"
diff --git a/composer.json b/composer.json
index 488db00..7c70d13 100644
--- a/composer.json
+++ b/composer.json
@@ -27,7 +27,7 @@
 	},
 	"require": {
 		"php": ">=7.1",
-		"phpunit/phpunit": "^7.5 || ^8.0 || ^9.0 || ^11.0"
+		"phpunit/phpunit": "^7.5 || ^8.0 || ^9.0 || ^11.0 || ^12.0"
 	},
 	"require-dev": {
 		"php-parallel-lint/php-console-highlighter": "^1.0.0",
@@ -90,7 +90,7 @@
 		"fix-cs": "Auto-fix code style violations in the PHP files.",
 		"test": "Run the unit tests without code coverage (PHPUnit < 10).",
 		"coverage": "Run the unit tests with code coverage (PHPUnit < 10).",
-		"test10": "Run the unit tests without code coverage using the PHPUnit 10/11 configuration file.",
-		"coverage10": "Run the unit tests with code coverage using the PHPUnit 10/11 configuration file."
+		"test10": "Run the unit tests without code coverage using the PHPUnit 10/11/12 configuration file.",
+		"coverage10": "Run the unit tests with code coverage using the PHPUnit 10/11/12 configuration file."
 	}
 }