diff --git a/src/Collection/CompletionWrapper.php b/src/Collection/CompletionWrapper.php
index 89aa5bb2f..b4a9428e2 100644
--- a/src/Collection/CompletionWrapper.php
+++ b/src/Collection/CompletionWrapper.php
@@ -54,7 +54,7 @@ class CompletionWrapper extends BaseTask implements WrappedTaskInterface
      * @param \Robo\Contract\TaskInterface $task
      * @param \Robo\Contract\TaskInterface|null $rollbackTask
      */
-    public function __construct(Collection $collection, TaskInterface $task, TaskInterface $rollbackTask = null)
+    public function __construct(Collection $collection, TaskInterface $task, ?TaskInterface $rollbackTask = null)
     {
         $this->collection = $collection;
         $this->task = ($task instanceof WrappedTaskInterface) ? $task->original() : $task;
diff --git a/src/Common/IO.php b/src/Common/IO.php
index a57def067..cd0ea7673 100644
--- a/src/Common/IO.php
+++ b/src/Common/IO.php
@@ -45,7 +45,7 @@ public function restore()
     }
 
     // This should typically only be called by State::restore()
-    public function restoreState(InputInterface $input = null, OutputInterface $output = null, SymfonyStyle $io = null)
+    public function restoreState(?InputInterface $input = null, ?OutputInterface $output = null, ?SymfonyStyle $io = null)
     {
         $this->setInput($input);
         $this->setOutput($output);