diff --git a/base/task.jl b/base/task.jl
index 76395cab5d7d2..b659c9e8594d0 100644
--- a/base/task.jl
+++ b/base/task.jl
@@ -412,7 +412,7 @@ end
 function enq_work(t::Task)
     (t.state == :runnable && t.queue === nothing) || error("schedule: Task not runnable")
     tid = Threads.threadid(t)
-    if t.sticky || tid != 0
+    if t.sticky || tid != 0 || Threads.nthreads() == 1
         if tid == 0
             tid = Threads.threadid()
         end
diff --git a/src/gc.c b/src/gc.c
index f1bc2d6f1e84c..0fe4b1fdc460a 100644
--- a/src/gc.c
+++ b/src/gc.c
@@ -2499,7 +2499,9 @@ static void mark_roots(jl_gc_mark_cache_t *gc_cache, jl_gc_mark_sp_t *sp)
     gc_mark_queue_obj(gc_cache, sp, jl_main_module);
 
     // tasks
+#ifdef JULIA_ENABLE_THREADING
     jl_gc_mark_enqueued_tasks(gc_cache, sp);
+#endif
 
     // invisible builtin values
     if (jl_an_empty_vec_any != NULL)
diff --git a/src/partr.c b/src/partr.c
index b11ff75f2bb3d..6fc672b0528e8 100644
--- a/src/partr.c
+++ b/src/partr.c
@@ -14,7 +14,19 @@
 extern "C" {
 #endif
 
-#define JULIA_ENABLE_PARTR
+
+// thread sleep state
+
+static int16_t sleep_check_state; // status of the multi-queue. possible values:
+
+// no thread should be sleeping--there might be work in the multi-queue.
+static const int16_t not_sleeping = 0;
+
+// it is acceptable for a thread to be sleeping if its sticky queue is empty.
+// sleep_check_state == sleeping + 1 + tid means thread tid is checking the multi-queue
+// to see if it is safe to transition to sleeping.
+static const int16_t sleeping = 1;
+
 
 #ifdef JULIA_ENABLE_THREADING
 
@@ -46,16 +58,6 @@ static int16_t heap_p;
 /* unbias state for the RNG */
 static uint64_t cong_unbias;
 
-static int16_t sleep_check_state; // status of the multi-queue. possible values:
-
-// no thread should be sleeping--there might be work in the multi-queue.
-static const int16_t not_sleeping = 0;
-
-// it is acceptable for a thread to be sleeping if its sticky queue is empty.
-// sleep_check_state == sleeping + 1 + tid means thread tid is checking the multi-queue
-// to see if it is safe to transition to sleeping.
-static const int16_t sleeping = 1;
-
 
 static inline void multiq_init(void)
 {
@@ -178,6 +180,15 @@ static inline jl_task_t *multiq_deletemin(void)
 }
 
 
+void jl_gc_mark_enqueued_tasks(jl_gc_mark_cache_t *gc_cache, jl_gc_mark_sp_t *sp)
+{
+    int16_t i, j;
+    for (i = 0; i < heap_p; ++i)
+        for (j = 0; j < heaps[i].ntasks; ++j)
+            jl_gc_mark_queue_obj_explicit(gc_cache, sp, (jl_value_t *)heaps[i].tasks[j]);
+}
+
+
 static int multiq_check_empty(void)
 {
     int16_t i;
@@ -275,6 +286,13 @@ void jl_threadfun(void *arg)
 }
 
 
+// enqueue the specified task for execution
+JL_DLLEXPORT void jl_enqueue_task(jl_task_t *task)
+{
+    multiq_insert(task, task->prio);
+}
+
+
 //  sleep_check_after_threshold() -- if sleep_threshold ns have passed, return 1
 static int sleep_check_after_threshold(uint64_t *start_cycles)
 {
@@ -301,6 +319,22 @@ static void wake_thread(int16_t self, int16_t tid)
     }
 }
 
+#else // JULIA_ENABLE_THREADING
+
+static int sleep_check_now(int16_t tid)
+{
+    (void)tid;
+    return 1;
+}
+
+static int sleep_check_after_threshold(uint64_t *start_cycles)
+{
+    (void)start_cycles;
+    return 1;
+}
+
+#endif
+
 /* ensure thread tid is awake if necessary */
 JL_DLLEXPORT void jl_wakeup_thread(int16_t tid)
 {
@@ -311,6 +345,7 @@ JL_DLLEXPORT void jl_wakeup_thread(int16_t tid)
         if (uvlock == self)
             uv_stop(jl_global_event_loop());
     }
+#ifdef JULIA_ENABLE_THREADING
     else {
         // check if the other threads might be sleeping
         if (jl_atomic_load_acquire(&sleep_check_state) != not_sleeping) {
@@ -333,13 +368,7 @@ JL_DLLEXPORT void jl_wakeup_thread(int16_t tid)
                 jl_wake_libuv();
         }
     }
-}
-
-
-// enqueue the specified task for execution
-JL_DLLEXPORT void jl_enqueue_task(jl_task_t *task)
-{
-    multiq_insert(task, task->prio);
+#endif
 }
 
 
@@ -356,7 +385,11 @@ static jl_task_t *get_next_task(jl_value_t *getsticky)
         }
         return task;
     }
+#ifdef JULIA_ENABLE_THREADING
     return multiq_deletemin();
+#else
+    return NULL;
+#endif
 }
 
 extern volatile unsigned _threadedregion;
@@ -373,11 +406,13 @@ JL_DLLEXPORT jl_task_t *jl_task_get_next(jl_value_t *getsticky)
         if (task)
             return task;
 
+#ifdef JULIA_ENABLE_THREADING
         jl_cpu_pause();
         if (!multiq_check_empty()) {
             start_cycles = 0;
             continue;
         }
+#endif
 
         jl_cpu_pause();
         if (sleep_check_after_threshold(&start_cycles) || (!_threadedregion && ptls->tid == 0)) {
@@ -465,17 +500,6 @@ JL_DLLEXPORT jl_task_t *jl_task_get_next(jl_value_t *getsticky)
     }
 }
 
-
-void jl_gc_mark_enqueued_tasks(jl_gc_mark_cache_t *gc_cache, jl_gc_mark_sp_t *sp)
-{
-    int16_t i, j;
-    for (i = 0; i < heap_p; ++i)
-        for (j = 0; j < heaps[i].ntasks; ++j)
-            jl_gc_mark_queue_obj_explicit(gc_cache, sp, (jl_value_t *)heaps[i].tasks[j]);
-}
-
-#endif // JULIA_ENABLE_THREADING
-
 #ifdef __cplusplus
 }
 #endif
diff --git a/src/task.c b/src/task.c
index e8a821e7f38fd..b5b633425d369 100644
--- a/src/task.c
+++ b/src/task.c
@@ -374,6 +374,8 @@ JL_DLLEXPORT void jl_switchto(jl_task_t **pt)
     assert(t->tid == ptls->tid);
     if (!t->sticky && !t->copy_stack)
         t->tid = -1;
+#elif defined(NDEBUG)
+    (void)refetch_ptls();
 #else
     assert(ptls == refetch_ptls());
 #endif
diff --git a/src/threading.c b/src/threading.c
index 7ce605f0ebeeb..caa477cdbfd12 100644
--- a/src/threading.c
+++ b/src/threading.c
@@ -505,15 +505,19 @@ JL_DLLEXPORT void jl_threading_run(jl_value_t *func)
         args2[0] = schd_func;
         args2[1] = (jl_value_t*)t;
         jl_apply(args2, 2);
+#ifdef JULIA_ENABLE_THREADING
         if (i == 1) {
             // let threads know work is coming (optimistic)
             jl_wakeup_thread(-1);
         }
+#endif
     }
+#ifdef JULIA_ENABLE_THREADING
     if (nthreads > 2) {
         // let threads know work is ready (guaranteed)
         jl_wakeup_thread(-1);
     }
+#endif
     // join with all tasks
     JL_TRY {
         for (int i = 0; i < nthreads; i++) {