diff --git a/filter_test.go b/filter_test.go
index d33b114..ad2e48c 100644
--- a/filter_test.go
+++ b/filter_test.go
@@ -16,6 +16,10 @@ func (m *mockFileInfo) Name() string {
 	return m.name
 }
 
+func (m *mockFileInfo) Sys() interface{} {
+	return nil
+}
+
 var _ os.FileInfo = &mockFileInfo{}
 
 func TestFileFilter(t *testing.T) {