diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index d335c47..6acbbc3 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -18,6 +18,7 @@ jobs:
           - '7.2'
           - '7.3'
           - '7.4'
+          - '8.0'
         deps:
           - highest
           - lowest
@@ -25,7 +26,7 @@ jobs:
     name: PHP ${{ matrix.php }} / ${{ matrix.deps }}
     steps:
       - uses: actions/checkout@v2
-      - uses: shivammathur/setup-php@151d1849c224dd5757287959c3c93f9e748f24d1
+      - uses: shivammathur/setup-php@4067ce8b814db5bfc731c8906aa3034f28911e9f
         with:
           php-version: ${{ matrix.php }}
       - name: Cache dependencies
@@ -59,10 +60,25 @@ jobs:
     name: PHP 5.3
     steps:
       - uses: actions/checkout@v2
-      - uses: shivammathur/setup-php@151d1849c224dd5757287959c3c93f9e748f24d1
+      - uses: shivammathur/setup-php@4067ce8b814db5bfc731c8906aa3034f28911e9f
         with:
           php-version: 5.3
-      - name: Parse ComposerPlugin.php
-        run: php -l src/ComposerPlugin.php
-      - name: Parse ComposerPlugin.fake.php
-        run: php -l src/ComposerPlugin.fake.php
+      - name: Syntax check
+        run: |
+          while read file; do
+            php -l "$file"
+          done < <(find src/Legacy -type f -name "*.php")
+      - name: Integration test
+        run: |
+          composer global config repositories.0 path "$(pwd)"
+          composer global require --ignore-platform-reqs cs278/composer-audit '*@dev'
+
+          set +e
+          composer global audit -vvv
+          result=$?
+          set -e
+
+          if [ $result -ne 2 ]; then
+            echo "Expected audit command to exit with error code 2, got: ${result}" >&2
+            exit 1
+          fi
diff --git a/composer.json b/composer.json
index 2eb3e54..07786dd 100644
--- a/composer.json
+++ b/composer.json
@@ -32,6 +32,6 @@
         "sort-packages": true
     },
     "extra": {
-        "class": "Cs278\\ComposerAudit\\ComposerPlugin"
+        "class": "Cs278\\ComposerAudit\\Legacy\\ComposerPlugin"
     }
 }
diff --git a/src/ComposerPlugin.fake.php b/src/ComposerPlugin.fake.php
deleted file mode 100644
index 927f1d0..0000000
--- a/src/ComposerPlugin.fake.php
+++ /dev/null
@@ -1,30 +0,0 @@
-<?php
-
-namespace Cs278\ComposerAudit;
-
-use Composer\Composer;
-use Composer\IO\IOInterface;
-use Composer\Plugin\PluginInterface;
-
-/**
- * Composer Audit Plugin declaration.
- *
- * @internal This class is used when loading the plugin with PHP < 7.1.
- */
-final class ComposerPlugin implements PluginInterface
-{
-    public function activate(Composer $composer, IOInterface $io)
-    {
-
-    }
-
-    public function deactivate(Composer $composer, IOInterface $io)
-    {
-
-    }
-
-    public function uninstall(Composer $composer, IOInterface $io)
-    {
-
-    }
-}
diff --git a/src/ComposerPlugin.php b/src/ComposerPlugin.php
index 1048abc..5530670 100644
--- a/src/ComposerPlugin.php
+++ b/src/ComposerPlugin.php
@@ -2,10 +2,36 @@
 
 namespace Cs278\ComposerAudit;
 
-if (!class_exists(__NAMESPACE__.'\\ComposerPlugin', false)) {
-    if (\PHP_VERSION_ID >= 70100) {
-        require __DIR__.'/ComposerPlugin.real.php';
-    } else {
-        require __DIR__.'/ComposerPlugin.fake.php';
+use Composer\Composer;
+use Composer\IO\IOInterface;
+use Composer\Plugin\PluginInterface;
+use Composer\Plugin\Capable;
+use Composer\Plugin\Capability\CommandProvider as CommandProviderCapability;
+
+/**
+ * Composer Audit Plugin declaration.
+ */
+final class ComposerPlugin implements PluginInterface, Capable
+{
+    public function activate(Composer $composer, IOInterface $io)
+    {
+
+    }
+
+    public function deactivate(Composer $composer, IOInterface $io)
+    {
+
+    }
+
+    public function uninstall(Composer $composer, IOInterface $io)
+    {
+
+    }
+
+    public function getCapabilities()
+    {
+        return [
+            CommandProviderCapability::class => CommandProvider::class,
+        ];
     }
 }
diff --git a/src/ComposerPlugin.real.php b/src/ComposerPlugin.real.php
deleted file mode 100644
index 5530670..0000000
--- a/src/ComposerPlugin.real.php
+++ /dev/null
@@ -1,37 +0,0 @@
-<?php
-
-namespace Cs278\ComposerAudit;
-
-use Composer\Composer;
-use Composer\IO\IOInterface;
-use Composer\Plugin\PluginInterface;
-use Composer\Plugin\Capable;
-use Composer\Plugin\Capability\CommandProvider as CommandProviderCapability;
-
-/**
- * Composer Audit Plugin declaration.
- */
-final class ComposerPlugin implements PluginInterface, Capable
-{
-    public function activate(Composer $composer, IOInterface $io)
-    {
-
-    }
-
-    public function deactivate(Composer $composer, IOInterface $io)
-    {
-
-    }
-
-    public function uninstall(Composer $composer, IOInterface $io)
-    {
-
-    }
-
-    public function getCapabilities()
-    {
-        return [
-            CommandProviderCapability::class => CommandProvider::class,
-        ];
-    }
-}
diff --git a/src/Legacy/AuditNotCompatibleCommand.php b/src/Legacy/AuditNotCompatibleCommand.php
new file mode 100644
index 0000000..f7488c3
--- /dev/null
+++ b/src/Legacy/AuditNotCompatibleCommand.php
@@ -0,0 +1,46 @@
+<?php
+
+namespace Cs278\ComposerAudit\Legacy;
+
+use Composer\Command\BaseCommand;
+use Symfony\Component\Console\Input\InputInterface;
+use Symfony\Component\Console\Input\InputOption;
+use Symfony\Component\Console\Output\ConsoleOutputInterface;
+use Symfony\Component\Console\Output\OutputInterface;
+
+/**
+ * Dummy command which tells the user they are using an unsupported PHP.
+ *
+ * @copyright 2021 Chris Smith
+ * @license MIT
+ */
+final class AuditNotCompatibleCommand extends BaseCommand
+{
+    protected function configure()
+    {
+        // Configuration is copied from AuditCommand so that the command accepts the same inputs.
+        $this->setName('audit');
+        $this->setDescription('Check packages for security advisories.');
+        $this->addOption(
+            'no-dev',
+            null,
+            InputOption::VALUE_NONE,
+            'Disable checking of development dependencies.'
+        );
+        $this->addOption(
+            'update',
+            null,
+            InputOption::VALUE_NONE,
+            'Update security advisory information if a new version is available.'
+        );
+    }
+
+    protected function execute(InputInterface $input, OutputInterface $output)
+    {
+        $output = $output instanceof ConsoleOutputInterface ? $output->getErrorOutput() : $output;
+
+        $output->writeln(sprintf('<error>Composer Audit is not compatible with PHP %s', PHP_VERSION));
+
+        return 2;
+    }
+}
diff --git a/src/Legacy/CommandProvider.php b/src/Legacy/CommandProvider.php
new file mode 100644
index 0000000..7b2e161
--- /dev/null
+++ b/src/Legacy/CommandProvider.php
@@ -0,0 +1,18 @@
+<?php
+
+namespace Cs278\ComposerAudit\Legacy;
+
+use Composer\Plugin\Capability\CommandProvider as CommandProviderCapability;
+
+/**
+ * @internal This class is used when loading the plugin with PHP < 7.1.
+ */
+final class CommandProvider implements CommandProviderCapability
+{
+    public function getCommands()
+    {
+        return array(
+            new AuditNotCompatibleCommand(),
+        );
+    }
+}
diff --git a/src/Legacy/ComposerPlugin.php b/src/Legacy/ComposerPlugin.php
new file mode 100644
index 0000000..b4055d6
--- /dev/null
+++ b/src/Legacy/ComposerPlugin.php
@@ -0,0 +1,44 @@
+<?php
+
+namespace Cs278\ComposerAudit\Legacy;
+
+use Composer\Composer;
+use Composer\IO\IOInterface;
+use Composer\Plugin\Capable;
+use Composer\Plugin\PluginInterface;
+
+if (!class_exists(__NAMESPACE__.'\\ComposerPlugin', false)) {
+    if (\PHP_VERSION_ID >= 70100) {
+        \class_alias(substr(__NAMESPACE__, 0, strrpos(__NAMESPACE__, '\\')).'\\ComposerPlugin', __NAMESPACE__.'\\ComposerPlugin');
+    } else {
+        /**
+         * Composer Audit Plugin declaration.
+         *
+         * @internal This class is used when loading the plugin with PHP < 7.1.
+         */
+        final class ComposerPlugin implements PluginInterface, Capable
+        {
+            public function activate(Composer $composer, IOInterface $io)
+            {
+
+            }
+
+            public function deactivate(Composer $composer, IOInterface $io)
+            {
+
+            }
+
+            public function uninstall(Composer $composer, IOInterface $io)
+            {
+
+            }
+
+            public function getCapabilities()
+            {
+                return array(
+                    'Composer\\Plugin\\Capability\\CommandProvider' => __NAMESPACE__.'\\CommandProvider',
+                );
+            }
+        }
+    }
+}
diff --git a/src/Legacy/README b/src/Legacy/README
new file mode 100644
index 0000000..22f42be
--- /dev/null
+++ b/src/Legacy/README
@@ -0,0 +1,2 @@
+Code in this namespace must be compatible with the lowest PHP version that
+Composer supports.