     /// Socket type not supported.
     public static var ESOCKTNOSUPPORT: POSIXError.Code { return .ESOCKTNOSUPPORT }
 
+    #if canImport(Darwin)
     /// Operation not supported.
     public static var ENOTSUP: POSIXError.Code { return .ENOTSUP }
+    #endif
 
     /// Protocol family not supported.
     public static var EPFNOSUPPORT: POSIXError.Code { return .EPFNOSUPPORT }

    /// Previous owner died.
    public static var EOWNERDEAD: POSIXError.Code { return .EOWNERDEAD }

    /// Interface output queue is full.
    public static var EQFULL: POSIXError.Code { return .EQFULL }
}

enum UnknownNSError: Error {

    /// STREAM ioctl timeout.
    public static var ETIME: POSIXError.Code { return .ETIME }

    #if canImport(Darwin)
    /// No such policy registered.
    public static var ENOPOLICY: POSIXError.Code { return .ENOPOLICY }
    #endif

    /// State not recoverable.
    public static var ENOTRECOVERABLE: POSIXError.Code { return .ENOTRECOVERABLE }
