"ReferenceError: lowercaseTypeName is not defined" for value types

I'm unable to use Q_GADGET + QML_VALUE_TYPE to declare a type with and enum exported to QML. At runtime I get this warning:
ReferenceError: lowercaseTypeName is not defined for value types

C++ code:
struct LowercaseTypeName
{{{}}
    Q_GADGET
    QML_VALUE_TYPE(lowercaseTypeName)

    enum Foo
    {
        BAR1,
        BAR2
    };
    Q_ENUM(Foo)
};

QML code:
property int value: 0
property bool is_bar1: value === lowercaseTypeName.BAR1

If I use QML_ELEMENT + QML_UNCREATABLE instead of QML_VALUE_TYPE then I get a different warning:
value type names should begin with a lowercase letter

Inheriting from QObject and using Q_OBJECT works OK.

The project uses QML modules in case it matters.