diff --git a/packages/postcss-merge-longhand/src/lib/clone.js b/packages/postcss-merge-longhand/src/lib/clone.js
index <HASH>..<HASH> 100644
--- a/packages/postcss-merge-longhand/src/lib/clone.js
+++ b/packages/postcss-merge-longhand/src/lib/clone.js
@@ -1,5 +1,5 @@
 export default function clone (obj, parent) {
-    if (typeof obj !== 'object') {
+    if (obj === null || typeof obj !== 'object') {
         return obj;
     }
     let cloned = new obj.constructor();
Resolve a crash when a cloned object was null.