diff --git a/tests/Scoper/Spec/SpecParser.php b/tests/Scoper/Spec/SpecParser.php
index e0019fbf..92d4a605 100644
--- a/tests/Scoper/Spec/SpecParser.php
+++ b/tests/Scoper/Spec/SpecParser.php
@@ -20,6 +20,7 @@
 use Humbug\PhpScoper\Configuration\SymbolsConfigurationFactory;
 use Humbug\PhpScoper\NotInstantiable;
 use InvalidArgumentException;
+use PHPUnit\Framework\Assert;
 use PHPUnit\Framework\Attributes\Group;
 use PHPUnit\Framework\TestCase;
 use Symfony\Component\Finder\SplFileInfo;
@@ -81,15 +82,19 @@ class SpecParser extends TestCase
     /**
      * @throws UnparsableFile
      */
-    public static function parseSpecFile(string $sourceDir, SplFileInfo $file): iterable
-    {
+    public static function parseSpecFile(
+        string $sourceDir,
+        SplFileInfo $file,
+    ): iterable {
         try {
-            $fixtures = include $file;
+            $specs = include $file;
+
+            self::checkSpecFileSchema($specs);
 
-            $meta = $fixtures['meta'];
-            unset($fixtures['meta']);
+            $meta = $specs['meta'];
+            unset($specs['meta']);
 
-            foreach ($fixtures as $fixtureTitle => $fixtureSet) {
+            foreach ($specs as $fixtureTitle => $fixtureSet) {
                 yield from self::parseSpec(
                     basename($sourceDir).'/'.$file->getRelativePathname(),
                     $meta,
@@ -102,6 +107,21 @@ public static function parseSpecFile(string $sourceDir, SplFileInfo $file): iter
         }
     }
 
+    /**
+     * @phpstan-assert array{'meta': array, array-key: string|array} $specs
+     */
+    private static function checkSpecFileSchema(mixed $specs): void
+    {
+        Assert::assertIsArray($specs);
+
+        Assert::assertArrayHasKey('meta', $specs);
+        Assert::assertIsArray($specs['meta']);
+
+        foreach ($specs as $title => $spec) {
+            Assert::assertTrue(is_string($spec) || is_array($spec));
+        }
+    }
+
     private static function parseSpec(
         string $file,
         array $meta,