diff --git a/reviewboard/static/rb/css/ui/discussion-header.less b/reviewboard/static/rb/css/ui/discussion-header.less
index 5612e93f915fa5495ea4ac8661508861c8ebba24..41ccbe08c410c6a139f341fdb7840cf24c054abb 100644
--- a/reviewboard/static/rb/css/ui/discussion-header.less
+++ b/reviewboard/static/rb/css/ui/discussion-header.less
@@ -48,6 +48,7 @@
 .rb-c-discussion-header {
   display: grid;
   gap: var(--ink-u-spacing-s);
+  width: 100%;
 
   /*
    * We'll align centered, and then align the text cells as baseline.