diff --git a/borgmatic/hooks/data_source/btrfs.py b/borgmatic/hooks/data_source/btrfs.py
index 0f7f46de..169f3061 100644
--- a/borgmatic/hooks/data_source/btrfs.py
+++ b/borgmatic/hooks/data_source/btrfs.py
@@ -134,6 +134,7 @@ def snapshot_subvolume(btrfs_command, subvolume_path, snapshot_path):  # pragma:
             btrfs_command,
             'subvolume',
             'snapshot',
+            '-r',  # Read-only,
             subvolume_path,
             snapshot_path,
         ),