diff --git a/src/queue.c b/src/queue.c
index 336c657..9c15faa 100644
--- a/src/queue.c
+++ b/src/queue.c
@@ -3667,8 +3667,9 @@ _dispatch_lane_drain(dispatch_lane_t dq, dispatch_invoke_context_t dic,
 			break;
 		}
 		if (likely(flags & DISPATCH_INVOKE_WORKLOOP_DRAIN)) {
-			dispatch_workloop_t dwl = (dispatch_workloop_t)_dispatch_get_wlh();
-			if (unlikely(_dispatch_queue_max_qos(dwl) > dwl->dwl_drained_qos)) {
+			// a workloop drained from a root queue thread has no workloop wlh
+			dispatch_workloop_t dwl = _dispatch_wlh_to_workloop(_dispatch_get_wlh());
+			if (dwl && unlikely(_dispatch_queue_max_qos(dwl) > dwl->dwl_drained_qos)) {
 				break;
 			}
 		}
@@ -5355,8 +5356,8 @@ _dispatch_channel_invoke_checks(dispatch_channel_t dch,
 		_dispatch_return_to_kernel();
 	}
 	if (likely(dcic->dcic_flags & DISPATCH_INVOKE_WORKLOOP_DRAIN)) {
-		dispatch_workloop_t dwl = (dispatch_workloop_t)_dispatch_get_wlh();
-		if (unlikely(_dispatch_queue_max_qos(dwl) > dwl->dwl_drained_qos)) {
+		dispatch_workloop_t dwl = _dispatch_wlh_to_workloop(_dispatch_get_wlh());
+		if (dwl && unlikely(_dispatch_queue_max_qos(dwl) > dwl->dwl_drained_qos)) {
 			dcic->dcic_tq = dch->do_targetq;
 			return false;
 		}