diff --git a/snapshot.js b/snapshot.js
index 26520bc..54a9784 100644
--- a/snapshot.js
+++ b/snapshot.js
@@ -153,7 +153,9 @@ async function milestoneTick() {
   const sc = X.siteConfig(); if (!sc.telegramBotToken) return null;
   const st = state(); const done = st.milestones || {};
   const count = await memberCount();
-  const due = marksUpTo(count).filter(m => !done[m]);
+  // presence of the key is what counts, never its value: a mark recorded as 0 (or any other
+  // falsy stamp) must stay done, or the ladder back-posts a number the site passed long ago
+  const due = marksUpTo(count).filter(m => !Object.prototype.hasOwnProperty.call(done, m));
   if (!due.length) return null;
   const mark = due[due.length - 1];
   const text = composeMilestone(mark, await gather(), sc.telegramCtaUrl);