diff --git a/src/components/post_status_form/post_status_form.js b/src/components/post_status_form/post_status_form.js
index 8c1fcef1c..e5d4451ef 100644
--- a/src/components/post_status_form/post_status_form.js
+++ b/src/components/post_status_form/post_status_form.js
@@ -305,7 +305,7 @@ const PostStatusForm = {
       target.style.height = 'auto'
       target.style.height = `${target.scrollHeight - vertPadding}px`
       if (target.value === '') {
-        target.style.height = undefined
+        target.style.height = null
       }
     },
     clearError () {