diff --git a/lib/svgo/js2svg.js b/lib/svgo/js2svg.js
index 5ae93e36..11ca3e3e 100644
--- a/lib/svgo/js2svg.js
+++ b/lib/svgo/js2svg.js
@@ -259,7 +259,7 @@ JS2SVG.prototype.createAttrs = function(elem) {
         attrs +=    ' ' +
                     attr.name +
                     this.config.attrStart +
-                    attr.value.replace(/"/g, '"') +
+                    String(attr.value).replace(/"/g, '"') +
                     this.config.attrEnd;
 
     }, this);