diff --git a/decimal.js b/decimal.js
index f7ecafb..1bb9a4a 100644
--- a/decimal.js
+++ b/decimal.js
@@ -936,7 +936,8 @@
     Ctor.precision = pr + 6;
     Ctor.rounding = 1;
 
-    x = x.div(new Ctor(1).minus(x.times(x)).sqrt().plus(1)).atan();
+    // See https://github.com/MikeMcl/decimal.js/issues/249
+    x = x.div(new Ctor(1).minus(x).times(new Ctor(1).plus(x)).sqrt().plus(1)).atan();
 
     Ctor.precision = pr;
     Ctor.rounding = rm;
diff --git a/decimal.mjs b/decimal.mjs
index 18dc640..522effa 100644
--- a/decimal.mjs
+++ b/decimal.mjs
@@ -932,7 +932,8 @@ P.inverseSine = P.asin = function () {
   Ctor.precision = pr + 6;
   Ctor.rounding = 1;
 
-  x = x.div(new Ctor(1).minus(x.times(x)).sqrt().plus(1)).atan();
+  // See https://github.com/MikeMcl/decimal.js/issues/249
+  x = x.div(new Ctor(1).minus(x).times(new Ctor(1).plus(x)).sqrt().plus(1)).atan();
 
   Ctor.precision = pr;
   Ctor.rounding = rm;
diff --git a/test/modules/asin.js b/test/modules/asin.js
index a5f7cd2..75f40c3 100644
--- a/test/modules/asin.js
+++ b/test/modules/asin.js
@@ -69,6 +69,12 @@ T('asin', function () {
   t('-0.5110799', 65, 2, '-0.53644070128325494453237503822033662227949443391067147724566337039');
   t('-0.579334355419195148', 31, 3, '-0.617911801796609232511609252874');
 
+  // Arguments very close to 1. See https://github.com/MikeMcl/decimal.js/issues/249
+  t('0.9999999999999999995', 31, 1, '1.570796325794896619231321691598');
+  t('0.99999999999999999999995', 36, 6, '1.5707963267848966192313216916397514');
+  t('-0.9999999999999999999', 30, 4, '-1.57079632634768302373136375235');
+  t('0.99999999999999999999999999999', 45, 0, '1.57079632679489214709536669206035862375124724');
+
   /*
   t('0.63', 1, 5, '0.7');
   t('-0.42', 4, 0, '-0.4335');