diff --git a/tools/lib/harness.mjs b/tools/lib/harness.mjs
index 555f3ff4..e5def6be 100644
--- a/tools/lib/harness.mjs
+++ b/tools/lib/harness.mjs
@@ -382,7 +382,8 @@ export async function runChecks(options, body) {
   let failures = 0;
   let checkCount = 0;
   function check(name, ok, detail = '') {
-    console.log(`${ok ? 'PASS' : 'FAIL'}  ${name}${detail ? ' – ' + detail : ''}`);
+    const text = typeof detail === 'string' ? detail : JSON.stringify(detail);
+    console.log(`${ok ? 'PASS' : 'FAIL'}  ${name}${text ? ' – ' + text : ''}`);
     checkCount++;
     if (!ok) failures++;
   }