diff --git a/src/ParallelTestRunner.jl b/src/ParallelTestRunner.jl
index 63b4eef..5283475 100644
--- a/src/ParallelTestRunner.jl
+++ b/src/ParallelTestRunner.jl
@@ -57,7 +57,7 @@ include("execute.jl")
              stderr = Base.stderr,
              max_worker_rss = get_max_worker_rss(),
              memory_per_worker = 2 * 2^30,
-             max_default_jobs = nothing,
+             max_default_jobs = typemax(Int64),
              serial = String[],
              serial_position::Symbol = :before,
              recycle_on_failure::Bool = false,
@@ -238,7 +238,7 @@ function runtests(mod::Module, args::ParsedArgs;
                   stderr = Base.stderr,
                   max_worker_rss = get_max_worker_rss(),
                   memory_per_worker = DEFAULT_MEMORY_PER_WORKER,
-                  max_default_jobs = nothing,
+                  max_default_jobs = DEFAULT_MAX_DEFAULT_JOBS,
                   recycle_on_failure::Bool = false,
                   retries::Integer = 0,
                   history_flush_every::Integer = 20,
@@ -341,7 +341,7 @@ function _runtests(mod::Module, args::ParsedArgs;
                    stderr = Base.stderr,
                    max_worker_rss = get_max_worker_rss(),
                    memory_per_worker = DEFAULT_MEMORY_PER_WORKER,
-                   max_default_jobs = nothing,
+                   max_default_jobs = DEFAULT_MAX_DEFAULT_JOBS,
                    recycle_on_failure::Bool = false,
                    retries::Integer = 0,
                    history_flush_every::Integer = 20,
@@ -352,14 +352,8 @@ function _runtests(mod::Module, args::ParsedArgs;
 
     # determine parallelism
     env_jobs = tryparse(Int, get(ENV, "PTR_NUM_JOBS", ""))
-    if max_default_jobs !== nothing
-        max_default_jobs isa Integer && !(max_default_jobs isa Bool) && max_default_jobs >= 1 ||
-            throw(ArgumentError("`max_default_jobs` must be a positive integer, got $(repr(max_default_jobs))"))
-    end
-    _jobs = @something args.jobs env_jobs begin
-        default_jobs = default_njobs(; memory_per_worker)
-        max_default_jobs === nothing ? default_jobs : min(default_jobs, max_default_jobs)
-    end
+
+    _jobs = _jobs = @something args.jobs env_jobs default_njobs(; memory_per_worker, max_default_jobs)
     jobs = clamp(_jobs, 1, max(1, length(parallel_tests)))
     worker_pool = Channel{Union{Nothing, PTRWorker}}(jobs)
     for _ in 1:jobs
diff --git a/src/resources.jl b/src/resources.jl
index f309531..177c513 100644
--- a/src/resources.jl
+++ b/src/resources.jl
@@ -35,6 +35,7 @@ end
 # memory). Packages whose tests are heavier can pass a larger
 # `memory_per_worker` to `runtests`.
 const DEFAULT_MEMORY_PER_WORKER = 2 * Int64(2)^30
+const DEFAULT_MAX_DEFAULT_JOBS = typemax(Int64)
 
 """
     default_njobs(; memory_per_worker = 2 * 2^30)
@@ -45,10 +46,14 @@ bytes of the available system memory.
 """
 function default_njobs(;
         memory_per_worker = DEFAULT_MEMORY_PER_WORKER,
+        max_default_jobs::Integer = DEFAULT_MAX_DEFAULT_JOBS,
         # Just use Sys.EFFECTIVE_CPU_THREADS when min VERSION >= v"1.13"
         _cpu_threads = (@static isdefined(Sys, :EFFECTIVE_CPU_THREADS) ? Sys.EFFECTIVE_CPU_THREADS : Sys.CPU_THREADS),
         _free_memory = available_memory(),
     )
+    !(max_default_jobs isa Bool) && max_default_jobs >= 1 ||
+        throw(ArgumentError("`max_default_jobs` must be a positive integer, got $(repr(max_default_jobs))"))
+
     memory_jobs = Int64(_free_memory) ÷ memory_per_worker
-    return max(1, min(_cpu_threads, memory_jobs))
+    return max(1, min(_cpu_threads, memory_jobs, max_default_jobs))
 end
diff --git a/test/core.jl b/test/core.jl
index 588ae5e..5e28a13 100644
--- a/test/core.jl
+++ b/test/core.jl
@@ -99,8 +99,12 @@ end
     end
     @test contains(String(take!(io)), "using 2 parallel jobs")
 
-    for bad in (0, -1, true, 1.5, "2")
+    for badint in (0, -1, true)
         @test_throws ArgumentError runtests(ParallelTestRunner, String[]; testsuite,
+                                            stdout=io, stderr=io, max_default_jobs=badint)
+    end
+    for bad in (1.5, "2")
+        @test_throws TypeError runtests(ParallelTestRunner, String[]; testsuite,
                                             stdout=io, stderr=io, max_default_jobs=bad)
     end
 end