diff --git a/packages/void/src/router/compile.ts b/packages/void/src/router/compile.ts
index 966e01dca..cc935bafd 100644
--- a/packages/void/src/router/compile.ts
+++ b/packages/void/src/router/compile.ts
@@ -903,7 +903,8 @@ export function compileRouteTable(
   lines.push('function __voidAnnotateRouting(response, trace) {');
   lines.push('  if (!__VOID_DEV_ROUTING || !response) return response;');
   lines.push('  const headers = new Headers(response.headers);');
-  lines.push('  headers.set("X-Void-Routing", trace);');
+  // Guard the set: a non-ASCII trace value throws, and must not crash the dev response.
+  lines.push('  try { headers.set("X-Void-Routing", trace); } catch { return response; }');
   lines.push(
     '  return new Response(response.body, { status: response.status, statusText: response.statusText, headers });',
   );
diff --git a/packages/void/test/unit/compile.test.ts b/packages/void/test/unit/compile.test.ts
index 97d028f78..e174bcb0f 100644
--- a/packages/void/test/unit/compile.test.ts
+++ b/packages/void/test/unit/compile.test.ts
@@ -1800,6 +1800,14 @@ describe('X-Void-Routing dev trace header', () => {
     expect(code).toContain('try { c.res.headers.set("X-Void-Routing", "pass-through"); } catch {}');
   });
 
+  it('guards the __voidAnnotateRouting trace header set with try/catch', () => {
+    const code = compileWith({ dev: true });
+    // A non-ASCII trace value throws on header set; the guard must swallow it.
+    expect(code).toContain(
+      'try { headers.set("X-Void-Routing", trace); } catch { return response; }',
+    );
+  });
+
   it('emits __VOID_DEV_ROUTING=false and strips origin fields in prod', () => {
     const code = compileWith({ dev: false });
     expect(code).toContain('const __VOID_DEV_ROUTING = false;');