diff --git a/lib/function/special/erf.js b/lib/function/special/erf.js
index da33ce349..652e3fa6c 100644
--- a/lib/function/special/erf.js
+++ b/lib/function/special/erf.js
@@ -1,7 +1,7 @@
 'use strict';
 
 var deepMap = require('../../utils/collection/deepMap');
-var isInteger = require('../../utils/number').isInteger;
+var sign = require('../../utils/number').sign;
 
 /**
  * Upper bound for the first approximation interval, 0 <= x <= THRESH
@@ -90,11 +90,11 @@ function factory (type, config, load, typed) {
       var y = Math.abs(x);
 
       if (y <= THRESH) {
-        return Math.sign(x) * erf1(y);
+        return sign(x) * erf1(y);
       } else if (y <= 4.0) {
-        return Math.sign(x) * (1 - erfc2(y));
+        return sign(x) * (1 - erfc2(y));
       } else {
-        return Math.sign(x) * (1 - erfc3(y));
+        return sign(x) * (1 - erfc3(y));
       }
     },