diff --git a/src/download/progress.test.ts b/src/download/progress.test.ts
new file mode 100644
index 000000000..441004e46
--- /dev/null
+++ b/src/download/progress.test.ts
@@ -0,0 +1,32 @@
+import { afterEach, describe, expect, it, vi } from 'vitest';
+import { createProgressBar } from './progress.js';
+
+describe('download progress display', () => {
+  afterEach(() => {
+    vi.restoreAllMocks();
+  });
+
+  it('clamps percentages above 100 to keep the progress bar renderable', () => {
+    const write = vi.spyOn(process.stderr, 'write').mockImplementation(() => true);
+    const progress = createProgressBar('file.bin', 0, 1);
+
+    expect(() => progress.update(150, 100)).not.toThrow();
+    expect(write).toHaveBeenCalledWith(expect.stringContaining('100%'));
+  });
+
+  it('clamps negative percentages to zero', () => {
+    const write = vi.spyOn(process.stderr, 'write').mockImplementation(() => true);
+    const progress = createProgressBar('file.bin', 0, 1);
+
+    expect(() => progress.update(-10, 100)).not.toThrow();
+    expect(write).toHaveBeenCalledWith(expect.stringContaining('0%'));
+  });
+
+  it('renders zero percent when the total size is unknown', () => {
+    const write = vi.spyOn(process.stderr, 'write').mockImplementation(() => true);
+    const progress = createProgressBar('file.bin', 0, 1);
+
+    expect(() => progress.update(50, 0)).not.toThrow();
+    expect(write).toHaveBeenCalledWith(expect.stringContaining('0%'));
+  });
+});
diff --git a/src/download/progress.ts b/src/download/progress.ts
index 972e4d836..352bfe284 100644
--- a/src/download/progress.ts
+++ b/src/download/progress.ts
@@ -47,7 +47,7 @@ export function createProgressBar(filename: string, index: number, total: number
 
   return {
     update(current: number, totalBytes: number, label?: string) {
-      const percent = totalBytes > 0 ? Math.round((current / totalBytes) * 100) : 0;
+      const percent = clampPercent(totalBytes > 0 ? Math.round((current / totalBytes) * 100) : 0);
       const bar = createBar(percent);
       const size = totalBytes > 0 ? formatBytes(totalBytes) : '';
       const extra = label ? ` ${label}` : '';
@@ -64,6 +64,11 @@ export function createProgressBar(filename: string, index: number, total: number
   };
 }
 
+function clampPercent(percent: number): number {
+  if (!Number.isFinite(percent)) return 0;
+  return Math.max(0, Math.min(100, percent));
+}
+
 /**
  * Create a progress bar string.
  */