--- a/src/core/ngx_core.h
+++ b/src/core/ngx_core.h
@@ -22,6 +22,10 @@ typedef struct ngx_event_s       ngx_eve
 typedef struct ngx_event_aio_s   ngx_event_aio_t;
 typedef struct ngx_connection_s  ngx_connection_t;
 
+#if (NGX_THREADS)
+typedef struct ngx_thread_task_s  ngx_thread_task_t;
+#endif
+
 typedef void (*ngx_event_handler_pt)(ngx_event_t *ev);
 typedef void (*ngx_connection_handler_pt)(ngx_connection_t *c);