diff --git a/composer.json b/composer.json
index c6fc0fe..c700d36 100644
--- a/composer.json
+++ b/composer.json
@@ -10,8 +10,8 @@
     ],
     "require": {
         "php": ">=7.4",
-        "symfony/process": "^5.2",
-        "symfony/event-dispatcher": "^5.2"
+        "symfony/process": "^4.0 || ^5.0",
+        "symfony/event-dispatcher": "^4.0 || ^5.0"
     },
     "autoload": {
         "psr-4": {
diff --git a/src/ProcessPool.php b/src/ProcessPool.php
index 4773ec3..f9338cc 100644
--- a/src/ProcessPool.php
+++ b/src/ProcessPool.php
@@ -126,10 +126,8 @@ private function shouldThrowExceptions(): bool
 
     /**
      * Get processes concurrency, default 5
-     *
-     * @return int
      */
-    public function getConcurrency()
+    public function getConcurrency(): int
     {
         return $this->concurrency;
     }
@@ -160,7 +158,7 @@ public function getEventDispatcher(): EventDispatcherInterface
     /**
      * @return static
      */
-    public function setEventDispatcher(EventDispatcher $eventDispatcher)
+    public function setEventDispatcher(EventDispatcherInterface $eventDispatcher)
     {
         $this->eventDispatcher = $eventDispatcher;