Index: kernel/generic/src/mm/backend_user.c
===================================================================
--- kernel/generic/src/mm/backend_user.c	(revision 174156fd1cf321a6363777352073d05829467b2f)
+++ kernel/generic/src/mm/backend_user.c	(revision e62f8e3fe3c6d4a7b8ff824766f6136e0e6ed0ed)
@@ -147,5 +147,5 @@
 	uintptr_t frame = IPC_GET_ARG1(data);
 	page_mapping_insert(AS, upage, frame, as_area_get_flags(area));
-	if (!used_space_insert(area, upage, 1))
+	if (!used_space_insert(&area->used_space, upage, 1))
 		panic("Cannot insert used space.");