diff --git a/roles/preflight/tasks/main.yml b/roles/preflight/tasks/main.yml
index d807f5f..4de2e40 100644
--- a/roles/preflight/tasks/main.yml
+++ b/roles/preflight/tasks/main.yml
@@ -8,7 +8,7 @@
 
 - name: Check disk space on critical mountpoints
   ansible.builtin.shell: |
-    df {{ item }} --output=pcent | tail -1 | tr -d ' %'
+    df -P {{ item }} | tail -1 | awk '{print $5}' | tr -d '%'  # POSIX flag — compatible with BusyBox (Alpine) and GNU coreutils
   register: disk_usage
   changed_when: false
   loop: