Index: generic/src/mm/backend_phys.c
===================================================================
--- generic/src/mm/backend_phys.c	(revision f8d069e88b964f4084aaf17a887ef7cdc28b63d2)
+++ generic/src/mm/backend_phys.c	(revision 722409391b4224fdf8543cea29d6131ebb5a6181)
@@ -65,10 +65,9 @@
 {
 	__address base = area->backend_data.base;
-	count_t frames = area->backend_data.frames;
 
 	if (!as_area_check_access(area, access))
 		return AS_PF_FAULT;
 
-	ASSERT(addr - area->base < frames * FRAME_SIZE);
+	ASSERT(addr - area->base < area->backend_data.frames * FRAME_SIZE);
 	page_mapping_insert(AS, addr, base + (addr - area->base), as_area_get_flags(area));
         if (!used_space_insert(area, ALIGN_DOWN(addr, PAGE_SIZE), 1))