diff --git a/src/static/js/charts.js b/src/static/js/charts.js
index c3fb24f..cee29a8 100644
--- a/src/static/js/charts.js
+++ b/src/static/js/charts.js
@@ -178,6 +178,12 @@ const ChartDefs = {
 
   timeline(sessions) {
     // Gantt-like bars: each session = one horizontal bar
+    // Filter out sessions with missing/invalid timestamps
+    sessions = sessions.filter(s => {
+      const st = new Date(s.start_at).getTime();
+      const en = new Date(s.end_at).getTime();
+      return st > 0 && en > 0 && !isNaN(st) && !isNaN(en) && en >= st;
+    });
     const labels = sessions.map(s => s.project_name.substring(0, 20));
     const starts = sessions.map(s => new Date(s.start_at).getTime());
     const ends = sessions.map(s => new Date(s.end_at).getTime());