diff --git a/src/core/ngx_thread_pool.c b/src/core/ngx_thread_pool.c
index 03530851a..f3655aa0b 100644
--- a/src/core/ngx_thread_pool.c
+++ b/src/core/ngx_thread_pool.c
@@ -345,6 +345,8 @@ ngx_thread_pool_cycle(void *data)
         *ngx_thread_pool_done.last = task;
         ngx_thread_pool_done.last = &task->next;
 
+        ngx_memory_barrier();
+
         ngx_unlock(&ngx_thread_pool_done_lock);
 
         (void) ngx_notify(ngx_thread_pool_handler);
@@ -366,6 +368,8 @@ ngx_thread_pool_handler(ngx_event_t *ev)
     ngx_thread_pool_done.first = NULL;
     ngx_thread_pool_done.last = &ngx_thread_pool_done.first;
 
+    ngx_memory_barrier();
+
     ngx_unlock(&ngx_thread_pool_done_lock);
 
     while (task) {