diff --git a/composer.json b/composer.json
index 8cecde7..5b9f626 100644
--- a/composer.json
+++ b/composer.json
@@ -7,7 +7,7 @@
         "php": "^7.0",
         "recoil/react": "^1.0",
         "recoil/recoil": "^1.0",
-        "nikic/php-parser": "^3.1",
+        "nikic/php-parser": "^4.0 || ^3.1",
         "psr/http-server-middleware": "^1.0"
     },
     "require-dev": {
diff --git a/src/YieldingMiddlewareFactory.php b/src/YieldingMiddlewareFactory.php
index 6b72809..d69c6a7 100644
--- a/src/YieldingMiddlewareFactory.php
+++ b/src/YieldingMiddlewareFactory.php
@@ -58,7 +58,7 @@ private static function iterateStmts(array $stmts, string $dir, string $file): a
                 $stmt->implements = [];
             }
 
-            if ($stmt instanceof ClassMethod && $stmt->name === 'process') {
+            if ($stmt instanceof ClassMethod && (string)$stmt->name === 'process') {
                 $stmt->returnType = null;
                 $stmt->params[1]->type = null;
             }