diff --git a/lib/function/utils/isPrime.js b/lib/function/utils/isPrime.js
index 3cf4c082a..155390910 100644
--- a/lib/function/utils/isPrime.js
+++ b/lib/function/utils/isPrime.js
@@ -1,7 +1,9 @@
 'use strict';
 
-var deepMap = require('../../utils/collection/deepMap');
-var number = require('../../utils/number');
+var deepMap = require('../../utils/collection/deepMap'),
+    number = require('../../utils/number'),
+    map = require('../../../index');
+
 
 function factory (type, config, load, typed) {
   /**
@@ -35,7 +37,7 @@ function factory (type, config, load, typed) {
   var isPrime = typed('isPrime', {
     'number': function (x) {
       if (x < 2){
-        return false
+        return false;
       }
       if (x == 2){
         return true;
@@ -53,17 +55,17 @@ function factory (type, config, load, typed) {
 
     // FIXME: use BigNumber methods instead of implicitely converting to number
     'BigNumber': function (x) {
-      if (x < 2){
-        return false
-      }
-      if (x == 2){
-        return true;
-      }
-      if (x % 2 == 0){ 
+      if (x.lt(2)){
         return false;
       }
-      for (var i = 3; i * i <= x; i += 2){
-        if (x % i == 0){
+      if (x.equals(2)){
+        return true;
+      }
+      if (x.mod(2).isZero()){
+        return false;
+      }
+      for(var i = type.BigNumber(3); i.times(i).lte(x); i = i.plus(1)){
+        if (x.mod(i).isZero()){
           return false;
         }
       }