diff --git a/Assets/UniGLTF/Runtime/Extensions/IndexExtensions.cs b/Assets/UniGLTF/Runtime/Extensions/IndexExtensions.cs
new file mode 100644
index 000000000..7599e5b95
--- /dev/null
+++ b/Assets/UniGLTF/Runtime/Extensions/IndexExtensions.cs
@@ -0,0 +1,19 @@
+namespace UniGLTF
+{
+    public static class IndexExtensions
+    {
+        public static bool HasValidIndex(this int? self)
+        {
+            if (!self.HasValue)
+            {
+                return false;
+            }
+            if (self.Value < 0)
+            {
+                // 古いモデルで index の無効値に -1 を使っている場合がある
+                return false;
+            }
+            return true;
+        }
+    }
+}
diff --git a/Assets/UniGLTF/Runtime/Extensions/IndexExtensions.cs.meta b/Assets/UniGLTF/Runtime/Extensions/IndexExtensions.cs.meta
new file mode 100644
index 000000000..c34759131
--- /dev/null
+++ b/Assets/UniGLTF/Runtime/Extensions/IndexExtensions.cs.meta
@@ -0,0 +1,11 @@
+fileFormatVersion: 2
+guid: e0989fbb259f59149ab310387ea69835
+MonoImporter:
+  externalObjects: {}
+  serializedVersion: 2
+  defaultReferences: []
+  executionOrder: 0
+  icon: {instanceID: 0}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 
diff --git a/Assets/UniGLTF/Runtime/UniGLTF/IO/BufferAccessor.cs b/Assets/UniGLTF/Runtime/UniGLTF/IO/BufferAccessor.cs
index 6ead44a56..faf01bfe1 100644
--- a/Assets/UniGLTF/Runtime/UniGLTF/IO/BufferAccessor.cs
+++ b/Assets/UniGLTF/Runtime/UniGLTF/IO/BufferAccessor.cs
@@ -318,7 +318,6 @@ namespace UniGLTF
                             componentType = (glComponentType)ComponentType,
                             type = AccessorType.ToString(),
                             count = Count,
-                            byteOffset = -1,
                             sparse = new glTFSparse
                             {
                                 count = sparseValuesWithIndex.Count,
diff --git a/Assets/UniGLTF/Runtime/UniGLTF/IO/GltfData.cs b/Assets/UniGLTF/Runtime/UniGLTF/IO/GltfData.cs
index 6e4feffe4..2a37c94b7 100644
--- a/Assets/UniGLTF/Runtime/UniGLTF/IO/GltfData.cs
+++ b/Assets/UniGLTF/Runtime/UniGLTF/IO/GltfData.cs
@@ -218,7 +218,7 @@ namespace UniGLTF
 
             if (vertexAccessor.count <= 0) return NativeArrayManager.CreateNativeArray<T>(0);
 
-            var result = (vertexAccessor.bufferView.HasValue)
+            var result = (vertexAccessor.bufferView.HasValidIndex())
                 ? GetTypedFromAccessor<T>(vertexAccessor, GLTF.bufferViews[vertexAccessor.bufferView.Value])
                 : NativeArrayManager.CreateNativeArray<T>(vertexAccessor.count)
                 ;
@@ -277,7 +277,7 @@ namespace UniGLTF
             var bufferCount = vertexAccessor.count * vertexAccessor.TypeCount;
 
             NativeArray<float> result = default;
-            if (vertexAccessor.bufferView.HasValue)
+            if (vertexAccessor.bufferView.HasValidIndex())
             {
                 var view = GLTF.bufferViews[vertexAccessor.bufferView.Value];
                 var segment = GetBytesFromBuffer(view.buffer);