diff --git a/web/src/renderer.js b/web/src/renderer.js
index ad49884..55ae7e2 100644
--- a/web/src/renderer.js
+++ b/web/src/renderer.js
@@ -302,11 +302,12 @@ export class RepoRenderer {
     // Watermark — tiled path text, 45° rotated, slightly larger than code font
     if (!tile.watermark) {
       const codeFontSize = (d.h / d.lines) * 0.65;
-      const wmFontSize = codeFontSize * 2.5;
+      // Clamp wmFontSize to avoid degenerate tiny values on files with huge line counts
+      const wmFontSize = Math.max(codeFontSize * 2.5, 1.0);
       const wmLabel = `${this.repoName}/${d.path}`;
-      // Estimate how many repetitions to fill the area
-      const charsPerLine = Math.ceil(Math.max(d.w, d.h) * 1.5 / (wmFontSize * 0.5));
-      const lineCount = Math.ceil(Math.max(d.w, d.h) * 1.5 / (wmFontSize * 1.5));
+      // Estimate how many repetitions to fill the area; cap to prevent RangeError on massive tiles
+      const charsPerLine = Math.min(Math.ceil(Math.max(d.w, d.h) * 1.5 / (wmFontSize * 0.5)), 400);
+      const lineCount = Math.min(Math.ceil(Math.max(d.w, d.h) * 1.5 / (wmFontSize * 1.5)), 150);
       const wmContent = buildWatermark(wmLabel, charsPerLine, lineCount);
 
       const wm = new Text();