diff --git a/packages/classnames/classnames.tsx b/packages/classnames/classnames.tsx
index 32207789..18db0a77 100644
--- a/packages/classnames/classnames.tsx
+++ b/packages/classnames/classnames.tsx
@@ -11,18 +11,24 @@
  *
  * @param strings classNames strings
  */
-export function classnames(...strings: Array<string | undefined>) {
+export function classnames(...strings: Array<string | undefined>): string;
+export function classnames() {
     let className = '';
     const uniqueCache = new Set();
-    const classNameList = strings.join(' ').split(' ');
+    // Use arguments instead rest operator for better performance.
+    const classNameList: Array<string | undefined> = [].slice.call(arguments);
 
     for (const value of classNameList) {
-        if (value === '' || uniqueCache.has(value)) {
+        if (value === '' || value === undefined || uniqueCache.has(value)) {
             continue;
         }
 
         uniqueCache.add(value);
-        if (className.length > 0) className += ' ';
+
+        if (className.length > 0) {
+            className += ' ';
+        }
+
         className += value;
     }