When trying to call a signal which expects a GValue argument, merely passing an integer constant is always going to create a TYPE_INT variant, which overflows when the constant is bigger than MAXINT. Depending on the API it might be better to automatically create a TYPE_INT64 variant?

The workaround is to create an explicit int64 value:

        v = GObject.Value()
        v.init(GObject.TYPE_INT64)
        v.set_int64(GObject.G_MAXINT64)

then you can pass v to a signal just fine (that's covered in a test case, see bug 683596).

In this case, the code path is the G_TYPE_BOXED case in pyg_value_from_pyobject() in gi/_gobject/pygtype.c, which calls pyg_type_from_object(), which does

       if (tp == &PYGLIB_PyLong_Type)
            return G_TYPE_INT;

i. e. does not do any range check.