diff --git a/src/Composer/Autoload/AutoloadGenerator.php b/src/Composer/Autoload/AutoloadGenerator.php
index a16e6b67b..734641d6d 100644
--- a/src/Composer/Autoload/AutoloadGenerator.php
+++ b/src/Composer/Autoload/AutoloadGenerator.php
@@ -720,6 +720,7 @@ EOF;
     protected function getPlatformCheck(array $packageMap, $checkPlatform, array $devPackageNames)
     {
         $lowestPhpVersion = Bound::zero();
+        $requiredPhp64bit = false;
         $requiredExtensions = [];
         $extensionProviders = [];
 
@@ -744,13 +745,17 @@ EOF;
                     continue;
                 }
 
-                if ('php' === $link->getTarget()) {
+                if (in_array($link->getTarget(), ['php', 'php-64bit'], true)) {
                     $constraint = $link->getConstraint();
                     if ($constraint->getLowerBound()->compareTo($lowestPhpVersion, '>')) {
                         $lowestPhpVersion = $constraint->getLowerBound();
                     }
                 }
 
+                if ('php-64bit' === $link->getTarget()) {
+                    $requiredPhp64bit = true;
+                }
+
                 if ($checkPlatform === true && Preg::isMatch('{^ext-(.+)$}iD', $link->getTarget(), $match)) {
                     // skip extension checks if they have a valid provider/replacer
                     if (isset($extensionProviders[$match[1]])) {
@@ -823,6 +828,16 @@ if (!($requiredPhp)) {
     \$issues[] = 'Your Composer dependencies require a PHP version $requiredPhpError. You are running ' . PHP_VERSION . '.';
 }
 
+PHP_CHECK;
+        }
+
+        if ($requiredPhp64bit) {
+            $requiredPhp .= <<<PHP_CHECK
+
+if (PHP_INT_SIZE !== 8) {
+    \$issues[] = 'Your Composer dependencies require a 64-bit build of PHP.';
+}
+
 PHP_CHECK;
         }
 
diff --git a/tests/Composer/Test/Autoload/AutoloadGeneratorTest.php b/tests/Composer/Test/Autoload/AutoloadGeneratorTest.php
index 134bcf222..e2bdd63ca 100644
--- a/tests/Composer/Test/Autoload/AutoloadGeneratorTest.php
+++ b/tests/Composer/Test/Autoload/AutoloadGeneratorTest.php
@@ -1861,6 +1861,18 @@ EOF;
                 ],
                 'specific_php_release',
             ],
+            'Specific 64-bit PHP version' => [
+                [
+                    'php-64bit' => new Link('a', 'php-64bit', $versionParser->parseConstraints('^7.2.8')),
+                ],
+                'specific_php_64bit_required',
+            ],
+            '64-bit PHP required' => [
+                [
+                    'php-64bit' => new Link('a', 'php-64bit', $versionParser->parseConstraints('*')),
+                ],
+                'php_64bit_required',
+            ],
             'No PHP required' => [
                 [
                     'ext-xml' => new Link('a', 'ext-xml', $versionParser->parseConstraints('*')),
diff --git a/tests/Composer/Test/Autoload/Fixtures/platform/php_64bit_required.php b/tests/Composer/Test/Autoload/Fixtures/platform/php_64bit_required.php
new file mode 100644
index 000000000..fa023908f
--- /dev/null
+++ b/tests/Composer/Test/Autoload/Fixtures/platform/php_64bit_required.php
@@ -0,0 +1,26 @@
+<?php
+
+// platform_check.php @generated by Composer
+
+$issues = array();
+
+if (PHP_INT_SIZE !== 8) {
+    $issues[] = 'Your Composer dependencies require a 64-bit build of PHP.';
+}
+
+if ($issues) {
+    if (!headers_sent()) {
+        header('HTTP/1.1 500 Internal Server Error');
+    }
+    if (!ini_get('display_errors')) {
+        if (PHP_SAPI === 'cli' || PHP_SAPI === 'phpdbg') {
+            fwrite(STDERR, 'Composer detected issues in your platform:' . PHP_EOL.PHP_EOL . implode(PHP_EOL, $issues) . PHP_EOL.PHP_EOL);
+        } elseif (!headers_sent()) {
+            echo 'Composer detected issues in your platform:' . PHP_EOL.PHP_EOL . str_replace('You are running '.PHP_VERSION.'.', '', implode(PHP_EOL, $issues)) . PHP_EOL.PHP_EOL;
+        }
+    }
+    trigger_error(
+        'Composer detected issues in your platform: ' . implode(' ', $issues),
+        E_USER_ERROR
+    );
+}
diff --git a/tests/Composer/Test/Autoload/Fixtures/platform/specific_php_64bit_required.php b/tests/Composer/Test/Autoload/Fixtures/platform/specific_php_64bit_required.php
new file mode 100644
index 000000000..fff78bb76
--- /dev/null
+++ b/tests/Composer/Test/Autoload/Fixtures/platform/specific_php_64bit_required.php
@@ -0,0 +1,30 @@
+<?php
+
+// platform_check.php @generated by Composer
+
+$issues = array();
+
+if (!(PHP_VERSION_ID >= 70208)) {
+    $issues[] = 'Your Composer dependencies require a PHP version ">= 7.2.8". You are running ' . PHP_VERSION . '.';
+}
+
+if (PHP_INT_SIZE !== 8) {
+    $issues[] = 'Your Composer dependencies require a 64-bit build of PHP.';
+}
+
+if ($issues) {
+    if (!headers_sent()) {
+        header('HTTP/1.1 500 Internal Server Error');
+    }
+    if (!ini_get('display_errors')) {
+        if (PHP_SAPI === 'cli' || PHP_SAPI === 'phpdbg') {
+            fwrite(STDERR, 'Composer detected issues in your platform:' . PHP_EOL.PHP_EOL . implode(PHP_EOL, $issues) . PHP_EOL.PHP_EOL);
+        } elseif (!headers_sent()) {
+            echo 'Composer detected issues in your platform:' . PHP_EOL.PHP_EOL . str_replace('You are running '.PHP_VERSION.'.', '', implode(PHP_EOL, $issues)) . PHP_EOL.PHP_EOL;
+        }
+    }
+    trigger_error(
+        'Composer detected issues in your platform: ' . implode(' ', $issues),
+        E_USER_ERROR
+    );
+}