diff --git a/polygerrit-ui/app/elements/gr-app-element_html.ts b/polygerrit-ui/app/elements/gr-app-element_html.ts
index 7dc6833932..c1258fb04b 100644
--- a/polygerrit-ui/app/elements/gr-app-element_html.ts
+++ b/polygerrit-ui/app/elements/gr-app-element_html.ts
@@ -40,8 +40,11 @@ export const htmlTemplate = html`
       border-left: 0;
       border-top: 0;
       box-shadow: var(--header-box-shadow);
-      /* Make sure the header is above the main content, to preserve box-shadow visibility */
-      z-index: 1;
+      /* Make sure the header is above the main content, to preserve box-shadow
+         visibility. We need 2 here instead of 1, because dropdowns in the
+         header should be shown on top of the sticky diff header, which has a
+         z-index of 1. */
+      z-index: 2;
     }
     footer {
       background: var(