diff --git a/.github/workflows/basics.yml b/.github/workflows/basics.yml
index 8ddeefbc..ccb9f0af 100644
--- a/.github/workflows/basics.yml
+++ b/.github/workflows/basics.yml
@@ -42,8 +42,8 @@ jobs:
         run: composer validate --no-check-all --strict
 
       - name: 'Composer: adjust dependencies'
-        # Using PHPCS `master` as an early detection system for bugs upstream.
-        run: composer require --no-update --no-scripts squizlabs/php_codesniffer:"dev-master" --no-interaction
+        # Using PHPCS `3.x` as an early detection system for bugs upstream.
+        run: composer require --no-update --no-scripts squizlabs/php_codesniffer:"3.x-dev" --no-interaction
 
       # Install dependencies and handle caching in one go.
       # @link https://github.com/marketplace/actions/install-php-dependencies-with-composer
@@ -74,17 +74,8 @@ jobs:
           pattern: ".phpcs.xml.dist"
           xsd-file: "vendor/squizlabs/php_codesniffer/phpcs.xsd"
 
-      # Notes:
-      # - PHPUnit 9.5 (which will be installed in this job) doesn't ship XSD files further back than 8.5.
-      # - PHPUnit 9.3 introduced some new configuration options and deprecated the old versions of those.
-      #   For cross-version compatibility with older PHPUnit versions, those new config options cannot be used yet,
-      #   which is why the PHPUnit 9 validation is done against the PHPUnit 9.2 schema.
-      - name: "Validate PHPUnit config for use with PHPUnit 8"
-        uses: phpcsstandards/xmllint-validate@v1
-        with:
-          pattern: "phpunit.xml.dist"
-          xsd-file: "vendor/phpunit/phpunit/schema/8.5.xsd"
-
+      # Note: PHPUnit 9.3 introduced some new configuration options and deprecated the old versions of those.
+      # For cross-version compatibility, the validation is done against the PHPUnit 9.2 schema.
       - name: "Validate PHPUnit config for use with PHPUnit 9"
         uses: phpcsstandards/xmllint-validate@v1
         with:
diff --git a/.github/workflows/quicktest.yml b/.github/workflows/quicktest.yml
index a020910d..1278e439 100644
--- a/.github/workflows/quicktest.yml
+++ b/.github/workflows/quicktest.yml
@@ -26,9 +26,9 @@ jobs:
     strategy:
       matrix:
         include:
-          - php: '5.4'
+          - php: '7.4'
             dependencies: 'stable'
-          - php: '5.4'
+          - php: '7.4'
             dependencies: 'lowest'
 
           - php: 'latest'
diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 30d84a10..7bfcf14e 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -28,7 +28,7 @@ jobs:
 
     strategy:
       matrix:
-        php: ['5.4', 'latest', '8.5']
+        php: ['7.4', 'latest', '8.5']
 
     name: "Lint: PHP ${{ matrix.php }}"
     continue-on-error: ${{ matrix.php == '8.5' }}
@@ -64,20 +64,13 @@ jobs:
       # - php: The PHP versions to test against.
       # - dependencies: The PHPCS dependencies versions to test against.
       #   IMPORTANT: test runs shouldn't fail because of PHPCS being incompatible with a PHP version.
-      #   - PHPCS will run without errors on PHP 5.4 - 7.4 on any supported version.
-      #   - PHP 8.0 needs PHPCS 3.5.7+ to run without errors, and we require a higher minimum version.
-      #   - PHP 8.1 needs PHPCS 3.6.1+ to run without errors, but works best with 3.7.1+, and we require at least this minimum version.
       #   - PHP 8.2, 8.3 and 8.4 need PHPCS 3.8.0+ to run without errors (though the errors don't affect the tests).
       matrix:
-        php: ['5.4', '5.5', '5.6', '7.0', '7.1', '7.2', '7.3', '7.4', '8.0', '8.1', '8.2', '8.3', '8.4']
+        php: ['7.4', '8.0', '8.1', '8.2', '8.3', '8.4']
         dependencies: ['lowest', 'stable']
 
         include:
           # Test against dev versions of all dependencies with select PHP versions for early detection of issues.
-          - php: '5.4'
-            dependencies: 'dev'
-          - php: '7.0'
-            dependencies: 'dev'
           - php: '7.4'
             dependencies: 'dev'
           - php: '8.4'
@@ -117,7 +110,7 @@ jobs:
         if: ${{ matrix.dependencies == 'dev' }}
         run: >
           composer require --no-update --no-scripts --no-interaction
-          squizlabs/php_codesniffer:"dev-master"
+          squizlabs/php_codesniffer:"3.x-dev"
           phpcsstandards/phpcsutils:"dev-develop"
           phpcsstandards/phpcsextra:"dev-develop"
           sirbrillig/phpcs-variable-analysis:"2.x"
diff --git a/composer.json b/composer.json
index 4579a657..bfe45898 100644
--- a/composer.json
+++ b/composer.json
@@ -16,7 +16,7 @@
 		}
 	],
 	"require": {
-		"php": ">=5.4",
+		"php": ">=7.4",
 		"phpcsstandards/phpcsextra": "^1.4.0",
 		"phpcsstandards/phpcsutils": "^1.1.0",
 		"sirbrillig/phpcs-variable-analysis": "^2.12.0",
@@ -28,7 +28,7 @@
 		"php-parallel-lint/php-console-highlighter": "^1.0.0",
 		"phpcompatibility/php-compatibility": "^9",
 		"phpcsstandards/phpcsdevtools": "^1.2.3",
-		"phpunit/phpunit": "^4 || ^5 || ^6 || ^7 || ^8 || ^9"
+		"phpunit/phpunit": "^9"
 	},
 	"config": {
 		"allow-plugins": {