diff --git a/test/index.js b/test/index.js
index e817d12..e1c4753 100644
--- a/test/index.js
+++ b/test/index.js
@@ -23,7 +23,10 @@ test ('random_hex with default length', (t) => {
 });
 
 test ('random_hex should refuse lenght smaller 1', (t) => {
-  t.throws (() => (crypto.random_hex (0)));
+  const error = t.throws (
+    () => (crypto.random_hex (0))
+  );
+  t.is(error.message, 'invalid length');
 });
 
 test ('random_string', (t) => {