diff --git a/composer.json b/composer.json
index 0fd2f70..334236d 100644
--- a/composer.json
+++ b/composer.json
@@ -12,7 +12,7 @@
 		}
 	],
 	"require": {
-		"php": ">=7.1.0",
+		"php": ">=7.3.0",
 		"ext-pcntl": "*",
 		"ext-posix": "*",
 		"ext-sysvsem": "*",
diff --git a/src/ProcessDetailsCollection.php b/src/ProcessDetailsCollection.php
index e34630b..4068e66 100644
--- a/src/ProcessDetailsCollection.php
+++ b/src/ProcessDetailsCollection.php
@@ -122,7 +122,8 @@ public function takeFreeProcess() : ?ProcessDetails {
 		if ($this->getFreeProcessesCount() === 0) {
 			return NULL;
 		}
-		$freePid = array_shift($this->freeProcessIds);
+		$freePid = array_key_first($this->freeProcessIds);
+		unset($this->freeProcessIds[$freePid]);
 		if ($freePid === NULL) {
 			return NULL;
 		}