diff --git a/src/Composer/Command/SelfUpdateCommand.php b/src/Composer/Command/SelfUpdateCommand.php
index 6ca01120c..1bf2e57d4 100644
--- a/src/Composer/Command/SelfUpdateCommand.php
+++ b/src/Composer/Command/SelfUpdateCommand.php
@@ -23,6 +23,7 @@ use Composer\SelfUpdate\Versions;
 use Composer\IO\IOInterface;
 use Composer\Downloader\FilesystemException;
 use Composer\Downloader\TransportException;
+use Phar;
 use Symfony\Component\Console\Input\InputInterface;
 use Composer\Console\Input\InputOption;
 use Composer\Console\Input\InputArgument;
@@ -116,9 +117,9 @@ EOT
         $cacheDir = $config->get('cache-dir');
         $rollbackDir = $config->get('data-dir');
         $home = $config->get('home');
-        $localFilename = realpath($_SERVER['argv'][0]);
-        if (false === $localFilename) {
-            $localFilename = $_SERVER['argv'][0];
+        $localFilename = Phar::running(false);
+        if ('' === $localFilename) {
+            throw new \RuntimeException('Could not determine the location of the composer.phar file as it appears you are not running this code from a phar archive.');
         }
 
         if ($input->getOption('update-keys')) {
diff --git a/tests/Composer/Test/AllFunctionalTest.php b/tests/Composer/Test/AllFunctionalTest.php
index 1ef22001d..f0de9d7c3 100644
--- a/tests/Composer/Test/AllFunctionalTest.php
+++ b/tests/Composer/Test/AllFunctionalTest.php
@@ -96,6 +96,7 @@ class AllFunctionalTest extends TestCase
 
         self::assertFileExists(self::$pharPath);
         copy(self::$pharPath, __DIR__.'/../../composer-test.phar');
+        chmod(__DIR__.'/../../composer-test.phar', 0777);
     }
 
     /**
diff --git a/tests/Composer/Test/Command/SelfUpdateCommandTest.php b/tests/Composer/Test/Command/SelfUpdateCommandTest.php
index d919dc9d6..3d2341c61 100644
--- a/tests/Composer/Test/Command/SelfUpdateCommandTest.php
+++ b/tests/Composer/Test/Command/SelfUpdateCommandTest.php
@@ -14,6 +14,7 @@ namespace Composer\Test\Command;
 
 use Composer\Composer;
 use Composer\Test\TestCase;
+use Symfony\Component\Process\Process;
 
 /**
  * @group slow
@@ -24,23 +25,15 @@ class SelfUpdateCommandTest extends TestCase
     /**
      * @var string
      */
-    private $prevArgv;
+    private $phar;
 
     public function setUp(): void
     {
         parent::setUp();
 
-        $this->prevArgv = $_SERVER['argv'][0];
         $dir = $this->initTempComposer();
         copy(__DIR__.'/../../../composer-test.phar', $dir.'/composer.phar');
-        $_SERVER['argv'][0] = $dir.'/composer.phar';
-    }
-
-    public function tearDown(): void
-    {
-        parent::tearDown();
-
-        $_SERVER['argv'][0] = $this->prevArgv;
+        $this->phar = $dir.'/composer.phar';
     }
 
     public function testSuccessfulUpdate(): void
@@ -49,20 +42,20 @@ class SelfUpdateCommandTest extends TestCase
             $this->markTestSkipped('On releases this test can fail to upgrade as we are already on latest version');
         }
 
-        $appTester = $this->getApplicationTester();
-        $appTester->run(['command' => 'self-update']);
+        $appTester = new Process([PHP_BINARY, $this->phar, 'self-update']);
+        $status = $appTester->run();
+        self::assertSame(0, $status, $appTester->getErrorOutput());
 
-        $appTester->assertCommandIsSuccessful();
-        self::assertStringContainsString('Upgrading to version', $appTester->getDisplay());
+        self::assertStringContainsString('Upgrading to version', $appTester->getOutput());
     }
 
     public function testUpdateToSpecificVersion(): void
     {
-        $appTester = $this->getApplicationTester();
-        $appTester->run(['command' => 'self-update', 'version' => '2.4.0']);
+        $appTester = new Process([PHP_BINARY, $this->phar, 'self-update', '2.4.0']);
+        $status = $appTester->run();
+        self::assertSame(0, $status, $appTester->getErrorOutput());
 
-        $appTester->assertCommandIsSuccessful();
-        self::assertStringContainsString('Upgrading to version 2.4.0', $appTester->getDisplay());
+        self::assertStringContainsString('Upgrading to version 2.4.0', $appTester->getOutput());
     }
 
     public function testUpdateWithInvalidOptionThrowsException(): void
@@ -83,12 +76,12 @@ class SelfUpdateCommandTest extends TestCase
             $this->markTestSkipped('On releases this test can fail to upgrade as we are already on latest version');
         }
 
-        $appTester = $this->getApplicationTester();
-        $appTester->run(['command' => 'self-update', $option => true]);
-        $appTester->assertCommandIsSuccessful();
+        $appTester = new Process([PHP_BINARY, $this->phar, 'self-update', $option]);
+        $status = $appTester->run();
+        self::assertSame(0, $status, $appTester->getErrorOutput());
 
-        self::assertStringContainsString('Upgrading to version', $appTester->getDisplay());
-        self::assertStringContainsString($expectedOutput, $appTester->getDisplay());
+        self::assertStringContainsString('Upgrading to version', $appTester->getOutput());
+        self::assertStringContainsString($expectedOutput, $appTester->getOutput());
     }
 
     /**