diff --git a/baselines/dom.generated.d.ts b/baselines/dom.generated.d.ts
index 3b106de41..69242be62 100644
--- a/baselines/dom.generated.d.ts
+++ b/baselines/dom.generated.d.ts
@@ -12454,10 +12454,10 @@ interface DocumentEvent {
 
 interface ElementTraversal {
     readonly childElementCount: number;
-    readonly firstElementChild: Element;
-    readonly lastElementChild: Element;
-    readonly nextElementSibling: Element;
-    readonly previousElementSibling: Element;
+    readonly firstElementChild: Element | null;
+    readonly lastElementChild: Element | null;
+    readonly nextElementSibling: Element | null;
+    readonly previousElementSibling: Element | null;
 }
 
 interface GetSVGDocument {
diff --git a/inputfiles/overridingTypes.json b/inputfiles/overridingTypes.json
index b9b40d469..c6640798f 100644
--- a/inputfiles/overridingTypes.json
+++ b/inputfiles/overridingTypes.json
@@ -929,5 +929,33 @@
         "kind": "extends",
         "baseInterface": "Node, GlobalEventHandlers, NodeSelector, DocumentEvent, ParentNode, DocumentOrShadowRoot",
         "interface": "Document"
+    },
+    {
+        "kind": "property",
+        "interface": "ElementTraversal",
+        "readonly": true,
+        "name": "firstElementChild",
+        "type": "Element | null"
+    },
+    {
+        "kind": "property",
+        "interface": "ElementTraversal",
+        "readonly": true,
+        "name": "lastElementChild",
+        "type": "Element | null"
+    },
+    {
+        "kind": "property",
+        "interface": "ElementTraversal",
+        "readonly": true,
+        "name": "nextElementSibling",
+        "type": "Element | null"
+    },
+    {
+        "kind": "property",
+        "interface": "ElementTraversal",
+        "readonly": true,
+        "name": "previousElementSibling",
+        "type": "Element | null"
     }
  ]