Enum members returned by `LspServerDescriptor.getWorkspaceConfiguration()` are serialized as numbers

IntelliJ Platform
,
1

I have a LspServerDescriptor whose getWorkspaceConfiguration looks something like this:

@Serializable
enum class E {
    @SerialName("a") A,
    @SerialName("b") B;
}

@Serializable
data class WorkspaceConfiguration(
    val choice: E
)

override fun getWorkspaceConfiguration(item: ConfigurationItem) =
    when (item.section) {
        "somekey" -> WorkspaceConfiguration(choice = E.A)
        else -> null
    }

Json.encodeToString(workspaceConfiguration) works as expected. Yet, here’s the actual workspace/configuration response:

[{ "choice": 0 }]

It seems enum members are serialized using their ordinals rather than names. Why is this the case and what can I do so that my custom serial names are respected?