diff --git a/test/modules/acos.js b/test/modules/acos.js
index 4537c33..b2ef48c 100644
--- a/test/modules/acos.js
+++ b/test/modules/acos.js
@@ -71,6 +71,7 @@ T('acos', function () {
   t('0.9999999297625', 14, 4, '0.00037479994883195');
   t('0.99999999467518', 14, 4, '0.0001031970930281');
   t('0.9999999999999999995', 25, 4, '0.000000001000000000000000000041667');
+  t('0.99999999999999999999995', 30, 4, '0.0000000000100000000000000000000000416667');
 
   /*
   t('0.95', 6, 5, '0.31756');