diff --git a/source/shell/mufs.c b/source/shell/mufs.c
index 8fa1fda..7871a13 100644
--- a/source/shell/mufs.c
+++ b/source/shell/mufs.c
@@ -73,6 +73,7 @@ static void do_mufs_unmount(const char *s)
 	if (flash) {
 		flash_release(flash);
 		flash = mufs->dev;
+		mufs->dev = NULL;
 	}
 
 	mufs_unmount(mufs);