diff --git a/lib/Controller/OccOutput.php b/lib/Controller/OccOutput.php
index d2f1829..5f0c0d0 100644
--- a/lib/Controller/OccOutput.php
+++ b/lib/Controller/OccOutput.php
@@ -19,7 +19,7 @@ class OccOutput extends BufferedOutput implements ConsoleOutputInterface
    *
    * @return OutputInterface
    */
-  public function getErrorOutput()
+  public function getErrorOutput(): OutputInterface
   {
     // TODO: Implement getErrorOutput() method.
     return $this;