diff --git a/src/main/java/org/kabeja/ui/model/adapter/DefaultLeafAdapter.java b/src/main/java/org/kabeja/ui/model/adapter/DefaultLeafAdapter.java
index dbbbbc6..1e5b3d9 100644
--- a/src/main/java/org/kabeja/ui/model/adapter/DefaultLeafAdapter.java
+++ b/src/main/java/org/kabeja/ui/model/adapter/DefaultLeafAdapter.java
@@ -30,7 +30,7 @@ public DefaultLeafAdapter(String name, TreeNode parent) {
     }
 
     @Override
-    public Enumeration<?> children() {
+    public Enumeration<? extends TreeNode> children() {
         return null;
     }
 
diff --git a/src/main/java/org/kabeja/ui/model/adapter/ProcessPipelinesAdapter.java b/src/main/java/org/kabeja/ui/model/adapter/ProcessPipelinesAdapter.java
index 71a2067..315986f 100644
--- a/src/main/java/org/kabeja/ui/model/adapter/ProcessPipelinesAdapter.java
+++ b/src/main/java/org/kabeja/ui/model/adapter/ProcessPipelinesAdapter.java
@@ -51,7 +51,7 @@ public int getChildCount() {
     }
 
     @Override
-    public Enumeration<?> children() {
+    public Enumeration<? extends TreeNode> children() {
         return null;
     }