diff --git a/.github/workflows/static.yml b/.github/workflows/static.yml
new file mode 100644
index 0000000..4e821aa
--- /dev/null
+++ b/.github/workflows/static.yml
@@ -0,0 +1,21 @@
+name: Static analysis
+
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+
+jobs:
+  phpstan:
+    name: PHPStan
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v2
+
+      - name: PHPStan
+        uses: docker://oskarstark/phpstan-ga
+        with:
+          args: analyze --no-progress
diff --git a/phpstan.neon.dist b/phpstan.neon.dist
new file mode 100644
index 0000000..776ccd8
--- /dev/null
+++ b/phpstan.neon.dist
@@ -0,0 +1,4 @@
+parameters:
+    level: max
+    paths:
+        - src
diff --git a/src/StopwatchPlugin.php b/src/StopwatchPlugin.php
index 96d35a2..01c2b52 100644
--- a/src/StopwatchPlugin.php
+++ b/src/StopwatchPlugin.php
@@ -4,6 +4,7 @@
 
 use Http\Client\Common\Plugin;
 use Http\Client\Exception;
+use Http\Promise\Promise;
 use Psr\Http\Message\RequestInterface;
 use Psr\Http\Message\ResponseInterface;
 use Symfony\Component\Stopwatch\Stopwatch;
@@ -29,17 +30,20 @@ public function __construct(Stopwatch $stopwatch)
         $this->stopwatch = $stopwatch;
     }
 
+    /**
+     * @return Promise Resolves a PSR-7 Response or fails with an Http\Client\Exception (The same as HttpAsyncClient)
+     */
     protected function doHandleRequest(RequestInterface $request, callable $next, callable $first)
     {
         $eventName = $this->getStopwatchEventName($request);
         $this->stopwatch->start($eventName, self::CATEGORY);
 
         return $next($request)->then(function (ResponseInterface $response) use ($eventName) {
-            $this->stopwatch->stop($eventName, self::CATEGORY);
+            $this->stopwatch->stop($eventName);
 
             return $response;
         }, function (Exception $exception) use ($eventName) {
-            $this->stopwatch->stop($eventName, self::CATEGORY);
+            $this->stopwatch->stop($eventName);
 
             throw $exception;
         });