diff --git a/features/scripts/utils/nomarchy-sys-update b/features/scripts/utils/nomarchy-sys-update
index cdbe83a..cb11f6e 100644
--- a/features/scripts/utils/nomarchy-sys-update
+++ b/features/scripts/utils/nomarchy-sys-update
@@ -15,8 +15,20 @@ else
     exit 1
 fi
 
-# Apply NixOS changes from the local flake
-echo "Applying system-level changes from $REPO_DIR..."
-sudo nixos-rebuild switch --flake "$REPO_DIR#default" --impure
+# The installer generates `nixosConfigurations.<hostname>` (see
+# installer/install.sh: `nixosConfigurations.$HOSTNAME`), so the flake target
+# must match the current host. The previous `#default` literal worked only
+# for a development host that happened to be named "default" and silently
+# broke every toggle script (nomarchy-tz-select, nomarchy-wifi-powersave,
+# nomarchy-setup-{dns,fido2,fingerprint}, nomarchy-toggle-hybrid-gpu) on a
+# real install.
+HOSTNAME_ATTR=$(hostname)
+if [ -z "$HOSTNAME_ATTR" ]; then
+    echo "Error: could not determine hostname for flake attribute." >&2
+    exit 1
+fi
+
+echo "Applying system-level changes from $REPO_DIR#$HOSTNAME_ATTR..."
+sudo nixos-rebuild switch --flake "$REPO_DIR#$HOSTNAME_ATTR"
 
 echo "System update complete."