diff --git a/src/Symfony/Component/Stopwatch/StopwatchEvent.php b/src/Symfony/Component/Stopwatch/StopwatchEvent.php
index 241572726cbf6..fc491e86d61f9 100644
--- a/src/Symfony/Component/Stopwatch/StopwatchEvent.php
+++ b/src/Symfony/Component/Stopwatch/StopwatchEvent.php
@@ -236,10 +236,7 @@ private function formatTime(float $time): float
         return round($time, 1);
     }
 
-    /**
-     * @return string
-     */
-    public function __toString()
+    public function __toString(): string
     {
         return sprintf('%s: %.2F MiB - %d ms', $this->getCategory(), $this->getMemory() / 1024 / 1024, $this->getDuration());
     }
diff --git a/src/Symfony/Component/Stopwatch/StopwatchPeriod.php b/src/Symfony/Component/Stopwatch/StopwatchPeriod.php
index 213cf59e12e89..b820d5ee3b077 100644
--- a/src/Symfony/Component/Stopwatch/StopwatchPeriod.php
+++ b/src/Symfony/Component/Stopwatch/StopwatchPeriod.php
@@ -73,4 +73,9 @@ public function getMemory()
     {
         return $this->memory;
     }
+
+    public function __toString(): string
+    {
+        return sprintf('%.2F MiB - %d ms', $this->getMemory() / 1024 / 1024, $this->getDuration());
+    }
 }