diff --git a/src/external/nacl-fast.js b/src/external/nacl-fast.js
index cb88475..a37ac0c 100644
--- a/src/external/nacl-fast.js
+++ b/src/external/nacl-fast.js
@@ -3,41 +3,44 @@
 
 
 // polyfill for TypedArray.prototype.slice()
-Uint8Array.prototype.slice = function(start, end) {
-	var len = this.length;
-	var relativeStart = start;
-	var k = (relativeStart < 0) ? max(len + relativeStart, 0) : Math.min(relativeStart, len);
-	var relativeEnd = (end === undefined) ? len : end;
-	var final = (relativeEnd < 0) ? max(len + relativeEnd, 0) : Math.min(relativeEnd, len);
-	var count = final - k;
-	var c = this.constructor;
-	var a = new c(count);
-	var n = 0;
-	while (k < final) {
-	    a[n] = JSON.parse(JSON.stringify(this[k]));
-	    k++;
-	    n++;
+if (!Uint8Array.prototype.slice) {
+	Uint8Array.prototype.slice = function(start, end) {
+		var len = this.length;
+		var relativeStart = start;
+		var k = (relativeStart < 0) ? Math.max(len + relativeStart, 0) : Math.min(relativeStart, len);
+		var relativeEnd = (end === undefined) ? len : end;
+		var final = (relativeEnd < 0) ? Math.max(len + relativeEnd, 0) : Math.min(relativeEnd, len);
+		var count = final - k;
+		var c = this.constructor;
+		var a = new c(count);
+		var n = 0;
+		while (k < final) {
+		    a[n] = JSON.parse(JSON.stringify(this[k]));
+		    k++;
+		    n++;
+		}
+		return a;
 	}
-	return a;
 }
 
-
-Float64Array.prototype.slice = function(start, end) {
-	var len = this.length;
-	var relativeStart = start;
-	var k = (relativeStart < 0) ? max(len + relativeStart, 0) : Math.min(relativeStart, len);
-	var relativeEnd = (end === undefined) ? len : end;
-	var final = (relativeEnd < 0) ? max(len + relativeEnd, 0) : Math.min(relativeEnd, len);
-	var count = final - k;
-	var c = this.constructor;
-	var a = new c(count);
-	var n = 0;
-	while (k < final) {
-	    a[n] = JSON.parse(JSON.stringify(this[k]));
-	    k++;
-	    n++;
+if (!Float64Array.prototype.slice) {
+	Float64Array.prototype.slice = function(start, end) {
+		var len = this.length;
+		var relativeStart = start;
+		var k = (relativeStart < 0) ? Math.max(len + relativeStart, 0) : Math.min(relativeStart, len);
+		var relativeEnd = (end === undefined) ? len : end;
+		var final = (relativeEnd < 0) ? Math.max(len + relativeEnd, 0) : Math.min(relativeEnd, len);
+		var count = final - k;
+		var c = this.constructor;
+		var a = new c(count);
+		var n = 0;
+		while (k < final) {
+		    a[n] = JSON.parse(JSON.stringify(this[k]));
+		    k++;
+		    n++;
+		}
+		return a;
 	}
-	return a;
 }
 
 // Ported in 2014 by Dmitry Chestnykh and Devi Mandiri.