diff --git a/src/Umbraco.Web.UI.Client/src/less/components/html/umb-expansion-panel.less b/src/Umbraco.Web.UI.Client/src/less/components/html/umb-expansion-panel.less
index ea08794c23..a686935c67 100644
--- a/src/Umbraco.Web.UI.Client/src/less/components/html/umb-expansion-panel.less
+++ b/src/Umbraco.Web.UI.Client/src/less/components/html/umb-expansion-panel.less
@@ -6,6 +6,7 @@
 }
 
 .umb-expansion-panel__header {
+    box-sizing: border-box;
     padding: 10px 20px;
     font-weight: bold;
     display: flex;