diff --git a/tests/discard/test-fstrim.pl b/tests/discard/test-fstrim.pl
index 30bb855b3..cec853fef 100755
--- a/tests/discard/test-fstrim.pl
+++ b/tests/discard/test-fstrim.pl
@@ -113,6 +113,8 @@ die "$0: surprising result: full size <= original size\n"
 # Remove the file and then try to trim the filesystem.
 
 $g->rm ("/data");
+$g->umount ("/");
+$g->mount_options ("nodiscard", "/dev/sda", "/");
 $g->fstrim ("/");
 $g->sync ();
 $g->close ();