diff --git a/block/blk-core.c b/block/blk-core.c
index 2bbf08c..5131993b 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1575,6 +1575,9 @@
  * @q: request_queue new bio is being queued at
  * @bio: new bio being queued
  * @request_count: out parameter for number of traversed plugged requests
+ * @same_queue_rq: pointer to &struct request that gets filled in when
+ * another request associated with @q is found on the plug list
+ * (optional, may be %NULL)
  *
  * Determine whether @bio being queued on @q can be merged with a request
  * on %current's plugged list.  Returns %true if merge was successful,