diff --git a/lib/jsbn.js b/lib/jsbn.js
index 11f965c5..9d59843a 100644
--- a/lib/jsbn.js
+++ b/lib/jsbn.js
@@ -117,7 +117,7 @@ function am3(i,x,w,j,c,n) {
 }
 
 // node.js (no browser)
-if(typeof(navigator) === 'undefined')
+if(forge.util.isNodejs)
 {
    BigInteger.prototype.am = am3;
    dbits = 28;