diff --git a/internal/web/static/paste-lines.js b/internal/web/static/paste-lines.js
index 231a473..c61ce21 100644
--- a/internal/web/static/paste-lines.js
+++ b/internal/web/static/paste-lines.js
@@ -77,7 +77,7 @@
     // gutter pass that changes the code column width reflows it. Verify the
     // placement one frame later and re-run if any line's row moved (#167).
     var placed = {};
-    for (var q = 0; q < tops.length; q++) placed[q] = Math.round((tops[q] - bodyTop) / lh);
+    for (var q = 0; q < rowIdx.length; q++) placed[q] = rowIdx[q];
     requestAnimationFrame(function () {
       var moved = false;
       var tops2 = [];