diff --git a/scripts/installer/auto-install.sh b/scripts/installer/auto-install.sh
index 9b7d273..93001f4 100755
--- a/scripts/installer/auto-install.sh
+++ b/scripts/installer/auto-install.sh
@@ -179,6 +179,21 @@ nixos-install \
     # makes boot stall waiting on the ZFS import. Exporting here (a no-op
     # if the chosen host has no ZFS root, e.g. proxmox-*/linode-*) clears
     # that in-use state so the next import, from any hostid, succeeds.
+    #
+    # nixos-install bind-mounts /dev, /proc, /sys (and usually /run) into
+    # /mnt to run the target's activation script (switch-to-configuration
+    # boot) in a chroot, and doesn't unmount them again once it's done.
+    # Left in place, those nested mounts make ZFS refuse to unmount its own
+    # root dataset at /mnt -- confirmed live: zpool export failed with
+    # "cannot unmount '/mnt': pool or dataset busy", and because of this
+    # script's `set -e`, that killed the script before it ever reached
+    # reboot, silently defeating the whole point of exporting first.
+    for chroot_mount in dev proc sys run; do
+        if mountpoint -q "/mnt/${chroot_mount}"; then
+            umount -R "/mnt/${chroot_mount}"
+        fi
+    done
+
     if [[ -n "$(zpool list -H -o name 2>/dev/null)" ]]; then
         echo "Exporting ZFS pool(s) before reboot..."
         zpool export -a