diff --git a/plugins/org.eclipse.glsp.graph/src/org/eclipse/glsp/graph/builder/GModelElementBuilder.java b/plugins/org.eclipse.glsp.graph/src/org/eclipse/glsp/graph/builder/GModelElementBuilder.java
index 58b661e4..bfc38c40 100644
--- a/plugins/org.eclipse.glsp.graph/src/org/eclipse/glsp/graph/builder/GModelElementBuilder.java
+++ b/plugins/org.eclipse.glsp.graph/src/org/eclipse/glsp/graph/builder/GModelElementBuilder.java
@@ -64,7 +64,7 @@ public E add(final GModelElement child) {
       return self();
    }
 
-   public E addAll(final List<GModelElement> children) {
+   public E addAll(final List<? extends GModelElement> children) {
       this.children.addAll(children);
       return self();
    }