diff --git a/src/private/pack_p.cpp b/src/private/pack_p.cpp
index 449e092..9419567 100644
--- a/src/private/pack_p.cpp
+++ b/src/private/pack_p.cpp
@@ -20,7 +20,7 @@ QReadWriteLock MsgPackPrivate::packers_lock;
 quint8 *MsgPackPrivate::pack(const QVariant &v, quint8 *p, bool wr, QVector<QByteArray> &user_data)
 {
     QMetaType::Type t = (QMetaType::Type)v.type();
-    if ((v.isNull() && !v.isValid()) || t == QMetaType::Nullptr)
+    if ((v.isNull() && !v.isValid()) || t == 51) // QMetaType::Nullptr
         p = pack_nil(p, wr);
     else if (t == QMetaType::Int)
         p = pack_int(v.toInt(), p, wr);