diff --git a/test/write_window_dirty_erase.c b/test/write_window_dirty_erase.c
index e839890..15f0bc3 100644
--- a/test/write_window_dirty_erase.c
+++ b/test/write_window_dirty_erase.c
@@ -5,6 +5,7 @@
 #include <sys/mman.h>
 
 #include "mboxd.h"
+#include "mtd/backend.h"
 #include "transport_mbox.h"
 
 #include "test/mbox.h"
@@ -114,7 +115,7 @@
 	assert(rc == 0);
 
 	map = mmap(NULL, MEM_SIZE, PROT_READ, MAP_PRIVATE,
-			ctx->fds[MTD_FD].fd, 0);
+			((struct mtd_data *)ctx->backend.priv)->fd, 0);
 	assert(map != MAP_FAILED);
 
 	rc = memcmp(flush_dirty_erased_dirty_data, map,