diff --git a/tests/Internal/NativeAdapter/ClassFixtures.php b/tests/Internal/NativeAdapter/ClassFixtures.php
index 86b6b08..80a3b5a 100644
--- a/tests/Internal/NativeAdapter/ClassFixtures.php
+++ b/tests/Internal/NativeAdapter/ClassFixtures.php
@@ -6,6 +6,94 @@
 
 final class ClassFixtures
 {
+    private const EXTENSIONS = [
+        'bcmath' => true,
+        'bz2' => true,
+        'calendar' => true,
+        'Core' => true,
+        'ctype' => true,
+        'curl' => true,
+        'date' => true,
+        'dba' => true,
+        'dom' => true,
+        'exif' => true,
+        'FFI' => true,
+        'fileinfo' => true,
+        'filter' => true,
+        'ftp' => true,
+        'gd' => true,
+        'gettext' => true,
+        'gmp' => true,
+        'hash' => true,
+        'iconv' => true,
+        'intl' => true,
+        'json' => true,
+        'ldap' => true,
+        'libxml' => true,
+        'mbstring' => true,
+        'mysqli' => true,
+        'mysqlnd' => true,
+        'odbc' => true,
+        'openssl' => true,
+        'pcntl' => true,
+        'pcov' => true,
+        'pcre' => true,
+        'PDO' => true,
+        'pdo_dblib' => true,
+        'pdo_mysql' => true,
+        'PDO_ODBC' => true,
+        'pdo_pgsql' => true,
+        'pdo_sqlite' => true,
+        'pgsql' => true,
+        'Phar' => true,
+        'posix' => true,
+        'pspell' => true,
+        'random' => true,
+        'readline' => true,
+        'Reflection' => true,
+        'session' => true,
+        'shmop' => true,
+        'SimpleXML' => true,
+        'soap' => true,
+        'sockets' => true,
+        'sodium' => true,
+        'SPL' => true,
+        'sqlite3' => true,
+        'standard' => true,
+        'sysvmsg' => true,
+        'sysvsem' => true,
+        'sysvshm' => true,
+        'tidy' => true,
+        'tokenizer' => true,
+        'xml' => true,
+        'xmlreader' => true,
+        'xmlwriter' => true,
+        'xsl' => true,
+        'Zend OPcache' => true,
+        'zip' => true,
+        'zlib' => true,
+    ];
+    private const INTERNAL_CLASSES_TO_SKIP = [
+        // has a private constructor that is available only via ReflectionClass::getConstructor()
+        'IntlCodePointBreakIterator' => true,
+        // ReflectionClass::getModifiers() returns 0 instead of 32 (enums have IS_FINAL)
+        'Random\IntervalBoundary' => true,
+        // is iterable, but does not implement Traversable
+        'FFI\CData' => true,
+        // has a lot of problems with __invoke()
+        'Closure' => true,
+        // getMethod(ispersistent).getNumberOfRequiredParameters(): failed asserting that 0 is identical to 2
+        'ZMQContext' => true,
+        // getMethod(remove).getNumberOfRequiredParameters(): failed asserting that 1 is identical to 2
+        'ZMQPoll' => true,
+        // Fatal error: OAuthProvider::__construct(): For the CLI sapi parameters must be set first via OAuthProvider::__construct(array("oauth_param" => "value", ...))
+        'OAuthProvider' => true,
+        // problems with readonly properties
+        'AMQPTimestamp' => true,
+        // problems with readonly properties
+        'AMQPDecimal' => true,
+    ];
+
     private function __construct() {}
 
     /**
@@ -41,26 +129,6 @@ public static function get(): array
 
         return self::$classes;
     }
-    private const INTERNAL_CLASSES_TO_SKIP = [
-        // has a private constructor that is available only via ReflectionClass::getConstructor()
-        'IntlCodePointBreakIterator' => true,
-        // ReflectionClass::getModifiers() returns 0 instead of 32 (enums have IS_FINAL)
-        'Random\IntervalBoundary' => true,
-        // is iterable, but does not implement Traversable
-        'FFI\CData' => true,
-        // has a lot of problems with __invoke()
-        'Closure' => true,
-        // getMethod(ispersistent).getNumberOfRequiredParameters(): failed asserting that 0 is identical to 2
-        'ZMQContext' => true,
-        // getMethod(remove).getNumberOfRequiredParameters(): failed asserting that 1 is identical to 2
-        'ZMQPoll' => true,
-        // Fatal error: OAuthProvider::__construct(): For the CLI sapi parameters must be set first via OAuthProvider::__construct(array("oauth_param" => "value", ...))
-        'OAuthProvider' => true,
-        // problems with readonly properties
-        'AMQPTimestamp' => true,
-        // problems with readonly properties
-        'AMQPDecimal' => true,
-    ];
 
     /**
      * @return \Generator<class-string, array{class-string}>
@@ -68,8 +136,10 @@ public static function get(): array
     public static function internal(): \Generator
     {
         foreach (self::allDeclaredClasses() as $class) {
+            $extension = (new \ReflectionClass($class))->getExtensionName();
+
             /** @psalm-suppress InvalidArrayOffset */
-            if (!isset(self::INTERNAL_CLASSES_TO_SKIP[$class]) && (new \ReflectionClass($class))->isInternal()) {
+            if ($extension !== false && !isset(self::INTERNAL_CLASSES_TO_SKIP[$class]) && isset(self::EXTENSIONS[$extension])) {
                 yield $class => [$class];
             }
         }