diff --git a/src/utils/joinClasses.js b/src/utils/joinClasses.js
index f6a5c9e4d3..5e610cf933 100644
--- a/src/utils/joinClasses.js
+++ b/src/utils/joinClasses.js
@@ -35,7 +35,9 @@ function joinClasses(className/*, ... */) {
   if (argLength > 1) {
     for (var ii = 1; ii < argLength; ii++) {
       nextClass = arguments[ii];
-      nextClass && (className += ' ' + nextClass);
+      if (nextClass) {
+        className = (className ? className + ' ' : '') + nextClass;
+      }
     }
   }
   return className;