diff --git a/static/app.js b/static/app.js
index b4b6d41..c68a865 100644
--- a/static/app.js
+++ b/static/app.js
@@ -1104,11 +1104,17 @@ createApp({
     }
 
     async function duplicateLine(line) {
-      if (line.geometry_resolved === false) return;
+      if (line.geometry_resolved === false) {
+        addEvent(`DUPLICATE #${line.number} FAILED · no source geometry`, 'error');
+        return;
+      }
       const anchorT = shiftTimeByBars(line, line.anchor_t);
       const endT = shiftTimeByBars(line, line.last_t);
       const cutoffT = line.cutoff_t == null ? null : shiftTimeByBars(line, line.cutoff_t);
-      if (anchorT == null || endT == null || (line.cutoff_t != null && cutoffT == null)) return;
+      if (anchorT == null || endT == null || (line.cutoff_t != null && cutoffT == null)) {
+        addEvent(`DUPLICATE #${line.number} FAILED · cannot shift 10 bars`, 'error');
+        return;
+      }
       const endP = line.anchor_p + line.slope * (line.last_t - line.anchor_t);
       const response = await apiFetch('/api/lines', {
         method: 'POST', headers: { 'Content-Type': 'application/json' },
@@ -1123,7 +1129,7 @@ createApp({
         }),
       });
       if (!response.ok) {
-        console.error(`Unable to duplicate line: HTTP ${response.status}`);
+        addEvent(`DUPLICATE #${line.number} FAILED · HTTP ${response.status}`, 'error');
         return;
       }
       const saved = await response.json();