diff --git a/mm/filemap.c b/mm/filemap.c
index c6ebd9f..e006c57 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -120,6 +120,7 @@
 	page->mapping = NULL;
 	mapping->nrpages--;
 	__dec_zone_page_state(page, NR_FILE_PAGES);
+	BUG_ON(page_mapped(page));
 }
 
 void remove_from_page_cache(struct page *page)