diff --git a/packages/edit-post/src/components/header/header-toolbar/index.js b/packages/edit-post/src/components/header/header-toolbar/index.js
index bcb81804272916..c4a33dacc01257 100644
--- a/packages/edit-post/src/components/header/header-toolbar/index.js
+++ b/packages/edit-post/src/components/header/header-toolbar/index.js
@@ -148,6 +148,7 @@ function HeaderToolbar() {
 					icon={ plus }
 					label={ showIconLabels ? shortLabel : longLabel }
 					showTooltip={ ! showIconLabels }
+					aria-expanded={ isInserterOpened }
 				/>
 				{ ( isWideViewport || ! showIconLabels ) && (
 					<>
diff --git a/packages/edit-site/src/components/header-edit-mode/index.js b/packages/edit-site/src/components/header-edit-mode/index.js
index 6cff62b94c51e3..b7652bd5e378f6 100644
--- a/packages/edit-site/src/components/header-edit-mode/index.js
+++ b/packages/edit-site/src/components/header-edit-mode/index.js
@@ -216,6 +216,7 @@ export default function HeaderEditMode() {
 									showIconLabels ? shortLabel : longLabel
 								}
 								showTooltip={ ! showIconLabels }
+								aria-expanded={ isInserterOpen }
 							/>
 						) }
 						{ isLargeViewport && (