diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 2f12c646..b6c26fa2 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -2,10 +2,10 @@ name: CI
 on:
   pull_request:
     branches:
-      - master
+      - main
   push:
     branches:
-      - master
+      - main
     tags: '*'
 jobs:
   test:
@@ -29,20 +29,11 @@ jobs:
         with:
           version: ${{ matrix.version }}
           arch: ${{ matrix.arch }}
-      - uses: actions/cache@v1
-        env:
-          cache-name: cache-artifacts
-        with:
-          path: ~/.julia/artifacts
-          key: ${{ runner.os }}-test-${{ env.cache-name }}-${{ hashFiles('**/Project.toml') }}
-          restore-keys: |
-            ${{ runner.os }}-test-${{ env.cache-name }}-
-            ${{ runner.os }}-test-
-            ${{ runner.os }}-
+      - uses: julia-actions/cache@v1
       - uses: julia-actions/julia-buildpkg@v1
       - uses: julia-actions/julia-runtest@v1
         env:
-          JULIA_NUM_THREADS: "3"
+          JULIA_NUM_THREADS: 4,1
       - uses: julia-actions/julia-processcoverage@v1
       - uses: codecov/codecov-action@v1
         with:
@@ -52,23 +43,10 @@ jobs:
     name: Documentation
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
-      - uses: julia-actions/setup-julia@v1
-        with:
-          version: '1.6'
-      - run: |
-          julia --project=docs -e '
-            using Pkg
-            Pkg.develop(PackageSpec(path=pwd()))
-            Pkg.instantiate()'
-      - run: |
-          julia --color=yes --project=docs/ -e '
-            using UnROOT
-            # using Pkg; Pkg.activate("docs")
-            using Documenter: DocMeta, doctest
-            DocMeta.setdocmeta!(UnROOT, :DocTestSetup, :(using UnROOT); recursive=true)
-            doctest(UnROOT)'
-      - run: julia --project=docs docs/make.jl
+      - uses: actions/checkout@v2
+      - uses: julia-actions/cache@v1
+      - uses: julia-actions/julia-buildpkg@latest
+      - uses: julia-actions/julia-docdeploy@latest
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
           DOCUMENTER_KEY: ${{ secrets.DOCUMENTER_KEY }}
diff --git a/Project.toml b/Project.toml
index 419a5516..56b55132 100644
--- a/Project.toml
+++ b/Project.toml
@@ -31,9 +31,9 @@ AbstractTrees = "^0.3.0, 0.4"
 ArraysOfArrays = "^0.5.3, ^0.6"
 Arrow = "2 - 2.5"
 BitIntegers = "^0.2.6, ^0.3"
-CodecLz4 = "^0.3.0, ^0.4.0"
-CodecXz = "^0.6.0, ^0.7.0"
-CodecZstd = "^0.6.0, ^0.7.0"
+CodecLz4 = "^0.3, ^0.4"
+CodecXz = "^0.6, ^0.7"
+CodecZstd = "^0.6, ^0.7, ^0.8"
 HTTP = "^0.9.7, 1"
 IterTools = "^1"
 LRUCache = "^1.3.0"
diff --git a/src/RNTuple/highlevel.jl b/src/RNTuple/highlevel.jl
index a1b95594..41848e24 100644
--- a/src/RNTuple/highlevel.jl
+++ b/src/RNTuple/highlevel.jl
@@ -19,9 +19,10 @@ struct RNTupleField{R, F, O, E} <: AbstractVector{E}
     function RNTupleField(rn::R, field::F) where {R, F}
         O = _field_output_type(F)
         E = eltype(O)
-        buffers = Vector{O}(undef, Threads.nthreads())
-        thread_locks = [ReentrantLock() for _ in 1:Threads.nthreads()]
-        buffer_ranges = [0:-1 for _ in 1:Threads.nthreads()]
+        Nthreads = _maxthreadid()
+        buffers = Vector{O}(undef, Nthreads)
+        thread_locks = [ReentrantLock() for _ in 1:Nthreads]
+        buffer_ranges = [0:-1 for _ in 1:Nthreads]
         new{R, F, O, E}(rn, field, buffers, thread_locks, buffer_ranges)
     end
 end
diff --git a/src/UnROOT.jl b/src/UnROOT.jl
index 3b6b5dbd..14236ec5 100644
--- a/src/UnROOT.jl
+++ b/src/UnROOT.jl
@@ -64,6 +64,13 @@ include("RNTuple/displays.jl")
 #     show(devnull, df)
 #     show(devnull, df[1])
 # end
+#
+
+_maxthreadid() = @static if VERSION < v"1.9"
+    Threads.nthreads()
+else
+    Threads.maxthreadid()
+end
 
 if VERSION >= v"1.9"
     let
diff --git a/src/bootstrap.jl b/src/bootstrap.jl
index 3091b930..1c5498e0 100644
--- a/src/bootstrap.jl
+++ b/src/bootstrap.jl
@@ -930,6 +930,12 @@ TH2F(io, tkey::TKey, refs) = TH(io, tkey, refs)
 TH1D(io, tkey::TKey, refs) = TH(io, tkey, refs)
 TH2D(io, tkey::TKey, refs) = TH(io, tkey, refs)
 
+"""
+    TH(io, tkey::TKey, refs)
+
+Internal function used to form a `fields = Dict{Symbol, Any}()` that represents the fields of a
+`TH` (histogram) in C++ ROOT.
+"""
 function TH(io, tkey::TKey, refs)
     fields = Dict{Symbol, Any}()
 
diff --git a/src/iteration.jl b/src/iteration.jl
index b4714e9b..b6f8832b 100644
--- a/src/iteration.jl
+++ b/src/iteration.jl
@@ -123,11 +123,12 @@ mutable struct LazyBranch{T,J,B} <: AbstractVector{T}
             _buffer = VectorOfVectors(T(), Int32[1])
             T = SubArray{eltype(T), 1, T, Tuple{UnitRange{Int64}}, true}
         end
+        Nthreads = _maxthreadid()
         return new{T,J,typeof(_buffer)}(f, b, length(b),
                                         b.fBasketEntry,
-                                        [_buffer for _ in 1:Threads.nthreads()],
-                                        [ReentrantLock() for _ in 1:Threads.nthreads()],
-                                        [0:-1 for _ in 1:Threads.nthreads()])
+                                        [_buffer for _ in 1:Nthreads],
+                                        [ReentrantLock() for _ in 1:Nthreads],
+                                        [0:-1 for _ in 1:Nthreads])
     end
 end
 LazyBranch(f::ROOTFile, s::AbstractString) = LazyBranch(f, f[s])
diff --git a/src/root.jl b/src/root.jl
index eadce273..fdd1ede2 100644
--- a/src/root.jl
+++ b/src/root.jl
@@ -38,6 +38,7 @@ function Base.hash(rf::ROOTFile, h::UInt)
     return hash(rf.fobj, h)
 end
 
+const HEAD_BUFFER_SIZE = 2048
 """
     ROOTFile(filename::AbstractString; customstructs = Dict("TLorentzVector" => LorentzVector{Float64}))
 
@@ -61,7 +62,6 @@ test/samples/NanoAODv5_sample.root
    └─ "⋮"
 ```
 """
-const HEAD_BUFFER_SIZE = 2048
 function ROOTFile(filename::AbstractString; customstructs = Dict("TLorentzVector" => LorentzVector{Float64}))
     fobj = if startswith(filename, r"https?://")
         HTTPStream(filename)
diff --git a/test/rntuple_tests.jl b/test/rntuple_tests.jl
index 1506b0f7..9b3d9b6b 100644
--- a/test/rntuple_tests.jl
+++ b/test/rntuple_tests.jl
@@ -157,8 +157,17 @@ end
     Threads.@threads for i in eachindex(field)
         @inbounds accumulator[Threads.threadid()] += field[i]
     end
+
     # test we've hit each thread's buffer
-    @test all(!isempty, field.buffers)
+    @test all(
+        map(eachindex(field.buffers)) do b
+            if !isassigned(field.buffers, b)
+                return true
+            else
+                return  !isempty(field.buffers[b])
+            end
+
+    end)
     @test sum(accumulator) == sum(1:5e4)
 
     accumulator .= 0
diff --git a/test/runtests.jl b/test/runtests.jl
index b2b66771..babb8fc2 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -4,7 +4,7 @@ using StaticArrays
 using InteractiveUtils
 using MD5
 
-const nthreads = Threads.nthreads()
+const nthreads = UnROOT._maxthreadid()
 nthreads == 1 && @warn "Running on a single thread. Please re-run the test suite with at least two threads (`julia --threads 2 ...`)"
 
 const SAMPLES_DIR = joinpath(@__DIR__, "samples")
@@ -766,13 +766,13 @@ end
 
 
     if get(ENV, "CI", "false") == "true"
-        if nthreads >= 1
-            @test Threads.nthreads()>1 
-        else
-            @warn "CI wasn't run with multi thread"
+        if nthreads == 1
+            @warn "CI wasn't run with multiple threads"
         end
     end
-    nmus = zeros(Int, Threads.nthreads())
+
+    nmus = zeros(Int, nthreads)
+
     Threads.@threads for i in 1:length(t)
         nmus[Threads.threadid()] += length(t.Muon_pt[i])
     end