diff --git a/base/condition.jl b/base/condition.jl
index 333075b7bfd6d..17d6b12f00df2 100644
--- a/base/condition.jl
+++ b/base/condition.jl
@@ -22,7 +22,6 @@ function trylock end
 function islocked end
 unlockall(l::AbstractLock) = unlock(l) # internal function for implementing `wait`
 relockall(l::AbstractLock, token::Nothing) = lock(l) # internal function for implementing `wait`
-assert_havelock(l::AbstractLock) = assert_havelock(l, Threads.threadid())
 assert_havelock(l::AbstractLock, tid::Integer) =
     (islocked(l) && tid == Threads.threadid()) ? nothing : concurrency_violation()
 assert_havelock(l::AbstractLock, tid::Task) =
diff --git a/base/lock.jl b/base/lock.jl
index 60066220b744e..ad728280c43e9 100644
--- a/base/lock.jl
+++ b/base/lock.jl
@@ -16,6 +16,7 @@ mutable struct ReentrantLock <: AbstractLock
     ReentrantLock() = new(nothing, GenericCondition{Threads.SpinLock}(), 0)
 end
 
+assert_havelock(l::ReentrantLock) = assert_havelock(l, l.locked_by)
 
 """
     islocked(lock) -> Status (Boolean)
diff --git a/base/locks-mt.jl b/base/locks-mt.jl
index 2ef1f8e2b2a67..a828adef1f913 100644
--- a/base/locks-mt.jl
+++ b/base/locks-mt.jl
@@ -30,6 +30,10 @@ struct SpinLock <: AbstractLock
     SpinLock() = new(Atomic{Int}(0))
 end
 
+# Note: this cannot assert that the lock is held by the correct thread, because we do not
+# track which thread locked it. Users beware.
+Base.assert_havelock(l::SpinLock) = islocked(l) ? nothing : concurrency_violation()
+
 function lock(l::SpinLock)
     while true
         if l.handle[] == 0
diff --git a/test/threads_exec.jl b/test/threads_exec.jl
index eb5ee45eb0972..2d6797fcf2600 100644
--- a/test/threads_exec.jl
+++ b/test/threads_exec.jl
@@ -151,6 +151,21 @@ end
 threaded_gc_locked(SpinLock)
 threaded_gc_locked(Threads.ReentrantLock)
 
+# Issue 33159
+# Make sure that a Threads.Condition can't be used without being locked, on any thread.
+@testset "Threads.Conditions must be locked" begin
+    c = Threads.Condition()
+    @test_throws Exception notify(c)
+    @test_throws Exception wait(c)
+
+    # If it's locked, but on the wrong thread, it should still throw an exception
+    lock(c)
+    @test_throws Exception fetch(@async notify(c))
+    @test_throws Exception fetch(@async notify(c, all=false))
+    @test_throws Exception fetch(@async wait(c))
+    unlock(c)
+end
+
 # Issue 14726
 # Make sure that eval'ing in a different module doesn't mess up other threads
 orig_curmodule14726 = @__MODULE__