diff --git a/libs/dnsx/naptr_service_test.go b/libs/dnsx/naptr_service_test.go
new file mode 100644
index 00000000..ffd62a96
--- /dev/null
+++ b/libs/dnsx/naptr_service_test.go
@@ -0,0 +1,13 @@
+package dnsx
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestNAPTRServiceTagValidation(t *testing.T) {
+	service := "SIP+D2U"
+	if !strings.Contains(service, "SIP") {
+		t.Fatalf("expected SIP service flag in NAPTR record, got %s", service)
+	}
+}