diff --git a/src/Command/DumpTreeCommand.php b/src/Command/DumpTreeCommand.php
index 8d240f7..e85659d 100644
--- a/src/Command/DumpTreeCommand.php
+++ b/src/Command/DumpTreeCommand.php
@@ -11,7 +11,7 @@ class DumpTreeCommand extends TreeCommand
 {
     private $shortOutput = false;
 
-    protected function configure()
+    protected function configure(): void
     {
         $this
             ->setName('webfactory:navigation:dump-tree')
diff --git a/src/Command/LookupNodeCommand.php b/src/Command/LookupNodeCommand.php
index 3163fab..34860d3 100644
--- a/src/Command/LookupNodeCommand.php
+++ b/src/Command/LookupNodeCommand.php
@@ -8,7 +8,7 @@
 
 class LookupNodeCommand extends TreeCommand
 {
-    protected function configure()
+    protected function configure(): void
     {
         $this
              ->setName('webfactory:navigation:lookup-node')