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/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/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 4edb1547..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")
@@ -766,18 +766,12 @@ end
 
 
     if get(ENV, "CI", "false") == "true"
-        if nthreads >= 1
-            @test Threads.nthreads()>1 
-        else
+        if nthreads == 1
             @warn "CI wasn't run with multiple threads"
         end
     end
 
-    nmus = if isdefined(Threads, :maxthreadid)
-        zeros(Int, Threads.maxthreadid())
-    else
-        zeros(Int, Threads.nthreads())
-    end
+    nmus = zeros(Int, nthreads)
 
     Threads.@threads for i in 1:length(t)
         nmus[Threads.threadid()] += length(t.Muon_pt[i])