diff --git a/src/Composer/Installer/BinaryInstaller.php b/src/Composer/Installer/BinaryInstaller.php
index d4470f4f0..91be81b54 100644
--- a/src/Composer/Installer/BinaryInstaller.php
+++ b/src/Composer/Installer/BinaryInstaller.php
@@ -255,17 +255,13 @@ class BinaryInstaller
         $binContents = file_get_contents($bin);
         // For php files, we generate a PHP proxy instead of a shell one,
         // which allows calling the proxy with a custom php process
-        if (preg_match('{^(?:#!(?:/usr)?/bin/env php|#!(?:/usr)?/bin/php|<?php)\r?\n}', $binContents, $match)) {
-            // verify the file is not a phar file, because those do not support php-proxying
-            if (false === ($pos = strpos($binContents, '__HALT_COMPILER')) || false === strpos(substr($binContents, 0, $pos), 'Phar::mapPhar')) {
-                $proxyCode = trim($match[0]);
-                // carry over the existing shebang if present, otherwise add our own
-                if ($proxyCode === "<?php") {
-                    $proxyCode = "#!/usr/bin/env php";
-                }
-                $binPathExported = var_export($binPath, true);
+        if (preg_match('{^(#!.*\r?\n)?<\?php}', $binContents, $match)) {
+            // carry over the existing shebang if present, otherwise add our own
+            $proxyCode = empty($match[1]) ? '#!/usr/bin/env php' : trim($match[1]);
+
+            $binPathExported = var_export($binPath, true);
 
-                return $proxyCode . "\n" . <<<PROXY
+            return $proxyCode . "\n" . <<<PROXY
 <?php
 
 /**
@@ -277,18 +273,95 @@ class BinaryInstaller
  * @generated
  */
 
+namespace Composer;
+
+\$binPath = __DIR__ . "/" . $binPathExported;
+
 if (PHP_VERSION_ID < 80000) {
-    ob_start(function (\$buffer, \$phase) {
-        return (PHP_OUTPUT_HANDLER_START & \$phase) && '#!' === substr(\$buffer, 0, 2) ? '' : \$buffer;
-    }, 1);
+    if (!class_exists('Composer\BinProxyWrapper')) {
+        /**
+         * @internal
+         */
+        final class BinProxyWrapper
+        {
+            private \$handle;
+            private \$position;
+
+            public function stream_open(\$path, \$mode, \$options, &\$opened_path)
+            {
+                // get rid of composer-bin-proxy:// prefix for __FILE__ & __DIR__ resolution
+                \$opened_path = substr(\$path, 21);
+                \$this->handle = fopen(\$opened_path, \$mode);
+                \$this->position = 0;
+
+                // remove all traces of this stream wrapper once it has been used
+                stream_wrapper_unregister('composer-bin-proxy');
+
+                return (bool) \$this->handle;
+            }
+
+            public function stream_read(\$count)
+            {
+                \$data = fread(\$this->handle, \$count);
+
+                if (\$this->position === 0) {
+                    \$data = preg_replace('{^#!.*\\r?\\n}', '', \$data);
+                }
+
+                \$this->position += strlen(\$data);
+
+                return \$data;
+            }
+
+            public function stream_cast(\$castAs)
+            {
+                return \$this->handle;
+            }
+
+            public function stream_close()
+            {
+                fclose(\$this->handle);
+            }
+
+            public function stream_lock(\$operation)
+            {
+                return \$operation ? flock(\$this->handle, \$operation) : true;
+            }
+
+            public function stream_tell()
+            {
+                return \$this->position;
+            }
+
+            public function stream_eof()
+            {
+                return feof(\$this->handle);
+            }
+
+            public function stream_stat()
+            {
+                return fstat(\$this->handle);
+            }
+
+            public function stream_set_option(\$option, \$arg1, \$arg2)
+            {
+                return true;
+            }
+        }
+    }
+
+    if (function_exists('stream_wrapper_register') && stream_wrapper_register('composer-bin-proxy', 'Composer\BinProxyWrapper')) {
+        include("composer-bin-proxy://" . \$binPath);
+        exit(0);
+    }
 }
 
-include __DIR__ . "/" . $binPathExported;
+include \$binPath;
+
 PROXY;
-            }
         }
 
-        $proxyCode = <<<PROXY
+        return <<<PROXY
 #!/usr/bin/env sh
 
 dir=\$(cd "\${0%[/\\\\]*}" > /dev/null; cd $binDir && pwd)
@@ -305,7 +378,5 @@ fi
 "\${dir}/$binFile" "\$@"
 
 PROXY;
-
-        return $proxyCode;
     }
 }
diff --git a/tests/Composer/Test/Installer/BinaryInstallerTest.php b/tests/Composer/Test/Installer/BinaryInstallerTest.php
new file mode 100644
index 000000000..b862556de
--- /dev/null
+++ b/tests/Composer/Test/Installer/BinaryInstallerTest.php
@@ -0,0 +1,136 @@
+<?php
+
+/*
+ * This file is part of Composer.
+ *
+ * (c) Nils Adermann <naderman@naderman.de>
+ *     Jordi Boggiano <j.boggiano@seld.be>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Composer\Test\Installer;
+
+use Composer\Installer\BinaryInstaller;
+use Composer\Util\Filesystem;
+use Composer\Test\TestCase;
+use Composer\Composer;
+use Composer\Config;
+use Composer\Util\ProcessExecutor;
+
+class BinaryInstallerTest extends TestCase
+{
+    /**
+     * @var string
+     */
+    protected $rootDir;
+
+    /**
+     * @var string
+     */
+    protected $vendorDir;
+
+    /**
+     * @var string
+     */
+    protected $binDir;
+
+    /**
+     * @var \Composer\IO\IOInterface&\PHPUnit\Framework\MockObject\MockObject
+     */
+    protected $io;
+
+    /**
+     * @var \Composer\Util\Filesystem
+     */
+    protected $fs;
+
+    protected function setUp()
+    {
+        $this->fs = new Filesystem;
+
+        $this->rootDir = $this->getUniqueTmpDirectory();
+        $this->vendorDir = $this->rootDir.DIRECTORY_SEPARATOR.'vendor';
+        $this->ensureDirectoryExistsAndClear($this->vendorDir);
+
+        $this->binDir = $this->rootDir.DIRECTORY_SEPARATOR.'bin';
+        $this->ensureDirectoryExistsAndClear($this->binDir);
+
+        $this->io = $this->getMockBuilder('Composer\IO\IOInterface')->getMock();
+    }
+
+    protected function tearDown()
+    {
+        $this->fs->removeDirectory($this->rootDir);
+    }
+
+    /**
+     * @dataProvider executableBinaryProvider
+     * @param string $contents
+     */
+    public function testInstallAndExecBinaryWithFullCompat($contents)
+    {
+        $package = $this->createPackageMock();
+        $package->expects($this->any())
+            ->method('getBinaries')
+            ->willReturn(array('binary'));
+
+        $this->ensureDirectoryExistsAndClear($this->vendorDir.'/foo/bar');
+        file_put_contents($this->vendorDir.'/foo/bar/binary', $contents);
+
+        $installer = new BinaryInstaller($this->io, $this->binDir, 'full', $this->fs);
+        $installer->installBinaries($package, $this->vendorDir.'/foo/bar');
+
+        $proc = new ProcessExecutor();
+        $proc->execute($this->binDir.'/binary arg', $output);
+        $this->assertEquals('', $proc->getErrorOutput());
+        $this->assertEquals('success arg', $output);
+    }
+
+    public function executableBinaryProvider()
+    {
+        $tests = array(
+            'simple php file' => array(<<<'EOL'
+<?php
+
+echo 'success '.$_SERVER['argv'][1];
+EOL
+            ),
+            'php file with shebang' => array(<<<'EOL'
+#!/usr/bin/env php
+<?php
+
+echo 'success '.$_SERVER['argv'][1];
+EOL
+            ),
+            'phar file' => array(
+                base64_decode('IyEvdXNyL2Jpbi9lbnYgcGhwCjw/cGhwCgpQaGFyOjptYXBQaGFyKCd0ZXN0LnBoYXInKTsKCnJlcXVpcmUgJ3BoYXI6Ly90ZXN0LnBoYXIvcnVuLnBocCc7CgpfX0hBTFRfQ09NUElMRVIoKTsgPz4NCj4AAAABAAAAEQAAAAEACQAAAHRlc3QucGhhcgAAAAAHAAAAcnVuLnBocCoAAADb9n9hKgAAAMUDDWGkAQAAAAAAADw/cGhwIGVjaG8gInN1Y2Nlc3MgIi4kX1NFUlZFUlsiYXJndiJdWzFdO1SOC0IE3+UN0yzrHIwyspp9slhmAgAAAEdCTUI=')
+            ),
+        );
+
+        if (PHP_VERSION_ID >= 70000) {
+            $tests += array(
+                'shebang with strict types declare' => array(<<<'EOL'
+#!/usr/bin/env php
+<?php declare(strict_types=1);
+
+echo 'success '.$_SERVER['argv'][1];
+EOL
+                ),
+            );
+        }
+
+        return $tests;
+    }
+
+    /**
+     * @return \Composer\Package\PackageInterface&\PHPUnit\Framework\MockObject\MockObject
+     */
+    protected function createPackageMock()
+    {
+        return $this->getMockBuilder('Composer\Package\Package')
+            ->setConstructorArgs(array(md5((string) mt_rand()), '1.0.0.0', '1.0.0'))
+            ->getMock();
+    }
+}