diff --git a/src/corelib/serialization/qdatastream.h b/src/corelib/serialization/qdatastream.h
index 2a5622f6030..71f2f4bbd9b 100644
--- a/src/corelib/serialization/qdatastream.h
+++ b/src/corelib/serialization/qdatastream.h
@@ -525,12 +525,21 @@ inline QDataStream &operator>>(QDataStream &s, QFlags<Enum> &e)
 template <typename T>
 typename std::enable_if_t<std::is_enum<T>::value, QDataStream &>
 operator<<(QDataStream &s, const T &t)
-{ return s << static_cast<typename std::underlying_type<T>::type>(t); }
+{
+    // std::underlying_type_t<T> may be long or ulong, for which QDataStream
+    // provides no streaming operators. For those, cast to qint64 or quint64.
+    return s << typename QIntegerForSizeof<T>::Unsigned(t);
+}
 
 template <typename T>
 typename std::enable_if_t<std::is_enum<T>::value, QDataStream &>
 operator>>(QDataStream &s, T &t)
-{ return s >> reinterpret_cast<typename std::underlying_type<T>::type &>(t); }
+{
+    typename QIntegerForSizeof<T>::Unsigned i;
+    s >> i;
+    t = T(i);
+    return s;
+}
 
 #ifndef Q_QDOC
 
diff --git a/tests/auto/corelib/serialization/qdatastream/tst_qdatastream.cpp b/tests/auto/corelib/serialization/qdatastream/tst_qdatastream.cpp
index 9a227c782de..0ff70ffb29a 100644
--- a/tests/auto/corelib/serialization/qdatastream/tst_qdatastream.cpp
+++ b/tests/auto/corelib/serialization/qdatastream/tst_qdatastream.cpp
@@ -3697,6 +3697,41 @@ void tst_QDataStream::enumTest()
     }
     ba.clear();
 
+    enum class E5 : qint64
+    {
+        A,
+        B,
+        C
+    };
+    {
+        QDataStream stream(&ba, QIODevice::WriteOnly);
+        stream << E5::C;
+        QCOMPARE(ba.size(), int(sizeof(E5)));
+    }
+    {
+        QDataStream stream(ba);
+        E5 e;
+        stream >> e;
+        QCOMPARE(e, E5::C);
+    }
+    ba.clear();
+
+    // unlike regular streaming operators, we accept long and ulong, because
+    // usually the only reason people see them is because they have
+    // std::(u)int64_t underlying types.
+    enum class ELong : long { A, B, C };
+    {
+        QDataStream stream(&ba, QIODevice::WriteOnly);
+        stream << ELong::A;
+        QCOMPARE(ba.size(), sizeof(long));
+    }
+    {
+        QDataStream stream(ba);
+        ELong e;
+        stream >> e;
+        QCOMPARE(e, ELong::A);
+    }
+    ba.clear();
 }
 
 void tst_QDataStream::floatingPointPrecision()