diff --git a/src/WatcherCommand.php b/src/WatcherCommand.php
index 8fa745e..4e2795e 100644
--- a/src/WatcherCommand.php
+++ b/src/WatcherCommand.php
@@ -34,7 +34,7 @@ protected function determineOptions(InputInterface $input): array
     {
         $options = $this->getOptionsFromConfigFile();
 
-        $commandLineArguments = trim($input->getArgument('phpunit-options'), "'");
+        $commandLineArguments = trim($input->getArgument('phpunit-options') ?? '', "'");
 
         if (! empty($commandLineArguments)) {
             $options['phpunit']['arguments'] = $commandLineArguments;