Threads.@threads over an iterator does not work - is there an reason?

julia> Threads.@threads for (index, value) in enumerate([1,2])
       end
ERROR: TaskFailedException
Stacktrace:
 [1] wait
   @ .\task.jl:322 [inlined]
 [2] threading_run(func::Function)
   @ Base.Threads .\threadingconstructs.jl:34
 [3] top-level scope
   @ .\threadingconstructs.jl:93

    nested task error: MethodError: no method matching firstindex(::Base.Iterators.Enumerate{Vector{Int64}})
    Closest candidates are:
      firstindex(::Any, ::Any) at abstractarray.jl:366
      firstindex(::Pair) at pair.jl:63
      firstindex(::UnitRange) at range.jl:567
      ...
    Stacktrace:
     [1] (::var"#36#threadsfor_fun#3"{Base.Iterators.Enumerate{Vector{Int64}}})(onethread::Bool)
       @ Main .\threadingconstructs.jl:66
     [2] (::var"#36#threadsfor_fun#3"{Base.Iterators.Enumerate{Vector{Int64}}})()
       @ Main .\threadingconstructs.jl:48

My current work around:

julia> Threads.@threads for (index, value) in collect(enumerate([1,2]))
       end