diff --git a/.github/workflows/ci-julia-nightly.yml b/.github/workflows/ci-julia-nightly.yml
index 7aaccae..01f6516 100644
--- a/.github/workflows/ci-julia-nightly.yml
+++ b/.github/workflows/ci-julia-nightly.yml
@@ -15,6 +15,11 @@ on:
       - 'LICENSE.md'
       - 'README.md'
       - '.github/workflows/TagBot.yml'
+  # Julia nightly changes without any change here (e.g. new LLVM versions, see #66),
+  # so also test it regularly.
+  schedule:
+    - cron: '17 4 * * 1'  # weekly, Monday 04:17 UTC
+  workflow_dispatch:
 jobs:
   test-julia-nightly:
     timeout-minutes: 30
diff --git a/src/threadtasks.jl b/src/threadtasks.jl
index 1ec5f29..695281b 100644
--- a/src/threadtasks.jl
+++ b/src/threadtasks.jl
@@ -61,12 +61,18 @@ end
 @noinline function wake_thread!(_tid::T) where {T<:Integer}
   tid = _tid % Int
   tidp1 = tid + one(tid)
+  # `Base.Workqueues` holds one queue per thread; `tidp1` must be a valid thread id.
+  # On Julia 1.13+ `Base.Workqueues` is a `OncePerThread`, and `Base.Workqueues()` is
+  # the *current* thread's queue, so its `length` is the number of queued tasks, not
+  # the number of threads. Assuming that count is `> tid` is false in general and lets
+  # LLVM 22 (Julia 1.14) miscompile the `length` loop (segfault).
   @static if VERSION >= v"1.13-"
-    assume(unsigned(length(Base.Workqueues())) > unsigned(tid))
+    assume(unsigned(Threads.maxthreadid()) > unsigned(tid))
   else
     assume(unsigned(length(Base.Workqueues)) > unsigned(tid))
   end
-  assume(unsigned(length(TASKS)) > unsigned(tidp1))
+  # `TASKS[tid]` is accessed below; `tid` ranges over `1:length(TASKS)`.
+  assume(unsigned(length(TASKS)) >= unsigned(tid))
   @inbounds push!(Base.Workqueues[tidp1], TASKS[tid])
   ccall(:jl_wakeup_thread, Cvoid, (Int16,), tid % Int16)
 end