diff --git a/btr/btr0cur.c b/btr/btr0cur.c
index dff30d77a7c..5fb21694940 100644
--- a/btr/btr0cur.c
+++ b/btr/btr0cur.c
@@ -2722,7 +2722,10 @@ btr_cur_optimistic_delete(
 				delete; cursor stays valid: if deletion
 				succeeds, on function exit it points to the
 				successor of the deleted record */
-	mtr_t*		mtr)	/* in: mtr */
+	mtr_t*		mtr)	/* in: mtr; if this function returns
+				TRUE on a leaf page of a secondary
+				index, the mtr must be committed
+				before latching any further pages */
 {
 	buf_block_t*	block;
 	rec_t*		rec;
diff --git a/include/btr0cur.h b/include/btr0cur.h
index 890d56f8fb6..e62bdb7b000 100644
--- a/include/btr0cur.h
+++ b/include/btr0cur.h
@@ -353,7 +353,10 @@ btr_cur_optimistic_delete(
 				cursor stays valid: if deletion succeeds,
 				on function exit it points to the successor
 				of the deleted record */
-	mtr_t*		mtr);	/* in: mtr */
+	mtr_t*		mtr);	/* in: mtr; if this function returns
+				TRUE on a leaf page of a secondary
+				index, the mtr must be committed
+				before latching any further pages */
 /*****************************************************************
 Removes the record on which the tree cursor is positioned. Tries
 to compress the page if its fillfactor drops below a threshold