diff --git a/psalm.xml b/psalm.xml
index 30258a7..030ec2f 100644
--- a/psalm.xml
+++ b/psalm.xml
@@ -1,7 +1,8 @@
 <?xml version="1.0"?>
 <psalm
-    errorLevel="3"
+    errorLevel="2"
     resolveFromConfigFile="true"
+    allowStringToStandInForClass="true"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xmlns="https://getpsalm.org/schema/config"
     xsi:schemaLocation="https://getpsalm.org/schema/config vendor/vimeo/psalm/config.xsd"
diff --git a/src/Dispatching/DispatchStack.php b/src/Dispatching/DispatchStack.php
index 17ae0e2..e7d9b56 100644
--- a/src/Dispatching/DispatchStack.php
+++ b/src/Dispatching/DispatchStack.php
@@ -10,7 +10,9 @@ use Psr\Http\Message\ServerRequestInterface;
  */
 class DispatchStack implements DispatchStackInterface
 {
+    /** @var mixed[] */
     private $stack;
+    /** @var DispatcherInterface */
     private $dispatcher;
 
     /**
@@ -66,7 +68,10 @@ class DispatchStack implements DispatchStackInterface
 
         // The final middleware's $next returns $response unchanged and sets
         // the $stackCompleted flag to indicate the stack has completed.
-        $chain = function ($request, $response) use (&$stackCompleted) {
+        $chain = function (
+            ServerRequestInterface $request,
+            ResponseInterface $response
+        ) use (&$stackCompleted): ResponseInterface {
             $stackCompleted = true;
             return $response;
         };
@@ -77,8 +82,16 @@ class DispatchStack implements DispatchStackInterface
         // contain a dispatcher, the associated middleware, and a $next function
         // that serves as the link to the next middleware in the chain.
         foreach (array_reverse($this->stack) as $middleware) {
-            $chain = function ($request, $response) use ($dispatcher, $middleware, $chain) {
-                return $dispatcher->dispatch($middleware, $request, $response, $chain);
+            $chain = function (
+                ServerRequestInterface $request,
+                ResponseInterface $response
+            ) use ($dispatcher, $middleware, $chain): ResponseInterface {
+                return $dispatcher->dispatch(
+                    $middleware,
+                    $request,
+                    $response,
+                    $chain
+                );
             };
         }
 
diff --git a/src/Dispatching/Dispatcher.php b/src/Dispatching/Dispatcher.php
index 5e6a76f..f420c4f 100644
--- a/src/Dispatching/Dispatcher.php
+++ b/src/Dispatching/Dispatcher.php
@@ -67,6 +67,10 @@ class Dispatcher implements DispatcherInterface
         }
     }
 
+    /**
+     * @param mixed[] $dispatchables
+     * @return DispatchStack
+     */
     protected function getDispatchStack($dispatchables)
     {
         $stack = new DispatchStack($this);