diff --git a/django/contrib/admin/static/admin/css/responsive.css b/django/contrib/admin/static/admin/css/responsive.css
index 2a6cccd56d..ef968c239e 100644
--- a/django/contrib/admin/static/admin/css/responsive.css
+++ b/django/contrib/admin/static/admin/css/responsive.css
@@ -217,7 +217,7 @@ input[type="submit"], button {
     }
 
     textarea {
-        max-width: 518px;
+        max-width: 100%;
         max-height: 120px;
     }
 
diff --git a/docs/releases/3.1.3.txt b/docs/releases/3.1.3.txt
index 300e4aff54..ce6cf962c7 100644
--- a/docs/releases/3.1.3.txt
+++ b/docs/releases/3.1.3.txt
@@ -53,3 +53,7 @@ Bugfixes
   reset tokens (:ticket:`32130`).
 
 * Added support for ``asgiref`` 3.3 (:ticket:`32128`).
+
+* Fixed a regression in Django 3.1 that caused incorrect textarea layout on
+  medium-sized screens in the admin change form view with the sidebar open
+  (:ticket:`32127`).