diff --git a/Process.php b/Process.php
index a4b0a784..62addf1e 100644
--- a/Process.php
+++ b/Process.php
@@ -352,7 +352,7 @@ public function start(?callable $callback = null, array $env = [])
 
         $this->process = @proc_open($commandline, $descriptors, $this->processPipes->pipes, $this->cwd, $envPairs, $this->options);
 
-        if (!\is_resource($this->process)) {
+        if (!$this->process) {
             throw new RuntimeException('Unable to launch a new process.');
         }
         $this->status = self::STATUS_STARTED;
@@ -1456,8 +1456,9 @@ private function readPipes(bool $blocking, bool $close)
     private function close(): int
     {
         $this->processPipes->close();
-        if (\is_resource($this->process)) {
+        if ($this->process) {
             proc_close($this->process);
+            $this->process = null;
         }
         $this->exitcode = $this->processInformation['exitcode'];
         $this->status = self::STATUS_TERMINATED;