diff --git a/src/utils/cx.ts b/src/utils/cx.ts
index 179b6d3..01ea737 100644
--- a/src/utils/cx.ts
+++ b/src/utils/cx.ts
@@ -1,18 +1,28 @@
+type CXValue = string | boolean | null | undefined
+
 /**
  * cx('class1', { class2: true, class3: false }) --> 'class1 class2'
  */
-export function cx(...classNames: any[]): string {
-  return classNames
-    .filter(Boolean)
-    .map(className => {
-      switch (typeof className) {
-        case 'string':
-          return className
-        case 'object':
-          return cx(...Object.entries(className).map(([key, value]) => (value ? key : null)))
-        default:
-          return ''
+export function cx(
+  ...classNames: (
+    | CXValue
+    | {
+        [className: string]: CXValue
       }
-    })
-    .join(' ')
+  )[]
+): string {
+  return classNames.map(handleClassName).filter(Boolean).join(' ')
+}
+
+function handleClassName(className: Parameters<typeof cx>[number]): string | false {
+  switch (typeof className) {
+    case 'string':
+      return className
+    case 'object':
+      return className === null
+        ? false
+        : cx(...Object.entries(className).map(([key, value]) => (value ? key : false)))
+    default:
+      return false
+  }
 }