diff --git a/src/modules/fstab/fstab.conf b/src/modules/fstab/fstab.conf
index 0e710980b..74b1feb39 100644
--- a/src/modules/fstab/fstab.conf
+++ b/src/modules/fstab/fstab.conf
@@ -11,6 +11,12 @@
 # Mount options to use for all filesystems. If a specific filesystem
 # is listed here, use those options, otherwise use the *default*
 # options from this mapping.
+#
+# With kernels 5.15 and newer be cautious of adding the option
+# space_cache to the btrfs mount options.  If the root volume is initially
+# mounted with one version of space_cache and the mount option specifies
+# a different version or implies v1 when v2 is in use, it may fail to
+# remount properly.
 mountOptions:
     default: defaults,noatime
     btrfs: defaults,noatime,autodefrag,compress=zstd