diff --git a/Assets/VRM/UniGLTF/Scripts/Format/glTF.cs b/Assets/VRM/UniGLTF/Scripts/Format/glTF.cs
index 2e0e4648a..7df4bd651 100644
--- a/Assets/VRM/UniGLTF/Scripts/Format/glTF.cs
+++ b/Assets/VRM/UniGLTF/Scripts/Format/glTF.cs
@@ -503,7 +503,10 @@ namespace UniGLTF
             string json;
             if (UseUniJSONSerializer)
             {
-                var c = new JsonSchemaValidationContext(this);
+                var c = new JsonSchemaValidationContext(this)
+                {
+                    EnableDiagnosisForNotRequiredFields = true,
+                };
                 json = JsonSchema.FromType(GetType()).Serialize(this, c);
             }
             else