diff --git a/src/lib/browser.test.ts b/src/lib/browser.test.ts
index 3d6717b..a5cb0ee 100644
--- a/src/lib/browser.test.ts
+++ b/src/lib/browser.test.ts
@@ -54,9 +54,16 @@ describe('openInBrowser', () => {
     expect(exec).not.toHaveBeenCalled();
   });
 
-  it('throws on a malformed URL', () => {
+  it('refuses a malformed URL with exit 5 before spawning', () => {
     const exec = vi.fn();
-    expect(() => openInBrowser('not a url', { exec })).toThrow();
+    let error: unknown;
+    try {
+      openInBrowser('not a url', { exec });
+    } catch (err) {
+      error = err;
+    }
+    expect(error).toBeInstanceOf(ApiError);
+    expect((error as ApiError).exitCode).toBe(5);
     expect(exec).not.toHaveBeenCalled();
   });
 
diff --git a/src/lib/browser.ts b/src/lib/browser.ts
index ccd2b8a..4d25823 100644
--- a/src/lib/browser.ts
+++ b/src/lib/browser.ts
@@ -23,7 +23,12 @@ export interface OpenInBrowserDeps {
 }
 
 export function openInBrowser(url: string, deps: OpenInBrowserDeps = {}): void {
-  const parsed = new URL(url);
+  let parsed: URL;
+  try {
+    parsed = new URL(url);
+  } catch {
+    throw localValidationError('url', 'must be a valid http(s) URL', undefined, 'field');
+  }
   if (parsed.protocol !== 'https:' && parsed.protocol !== 'http:') {
     // User-input error, not an internal failure: classify as VALIDATION_ERROR
     // so it maps to exit 5 (like every other bad-argument path), not exit 1.