diff --git a/model_loader/model_loader.go b/model_loader/model_loader.go
index 1a608d6..ede11dc 100644
--- a/model_loader/model_loader.go
+++ b/model_loader/model_loader.go
@@ -170,7 +170,7 @@ func loadValue(key string, arg interface{}, field reflect.Value) error {
 func getFieldByName(model reflect.Value, name string) (reflect.Value, error) {
 	field := model.Elem().FieldByName(name)
 	if !field.IsValid() {
-		return reflect.ValueOf(nil), fmt.Errorf("Field `%s` does not exist.", name)
+		return reflect.ValueOf(nil), fmt.Errorf("Unknown option or argument: `%s`.", name)
 	}
 	return field, nil
 }
diff --git a/model_loader/model_loader_test.go b/model_loader/model_loader_test.go
index c261a40..7d13293 100644
--- a/model_loader/model_loader_test.go
+++ b/model_loader/model_loader_test.go
@@ -199,7 +199,7 @@ var testCases = []modelLoaderTestCase{
 		args: map[string]interface{}{
 			"UnknownField": "some value",
 		},
-		err: "Field `UnknownField` does not exist.",
+		err: "Unknown option or argument: `UnknownField`.",
 	},
 	// Fails with different type mismatches.
 	{