diff --git a/src/Storage/Mbox.php b/src/Storage/Mbox.php
index 3e48a6c6..52f6bcfe 100644
--- a/src/Storage/Mbox.php
+++ b/src/Storage/Mbox.php
@@ -308,7 +308,9 @@ protected function openMboxFile($filename)
     public function close()
     {
         ErrorHandler::start(E_WARNING);
-        fclose($this->fh);
+        if (is_resource($this->fh)) {
+            fclose($this->fh);
+        }
         ErrorHandler::stop();
         $this->positions = [];
     }