diff --git a/mail/templates/default/app.css b/mail/templates/default/app.css
index 96746a9f21..108f682ed6 100644
--- a/mail/templates/default/app.css
+++ b/mail/templates/default/app.css
@@ -1048,6 +1048,7 @@ div#mail-index_nm.splitter-pane {min-height: 100px;}
 .previewWrapper .firstColumnTitle {
 	max-width: 4em;
 	text-align: end;
+	min-width: 4em;
 }
 .mailPreviewHeaders et2-select-email::part(control) {
 	border: none;