diff --git a/packages/block-library/src/navigation/frontend.js b/packages/block-library/src/navigation/frontend.js
index 592106763e4825..1bf1f9fa3a51fc 100644
--- a/packages/block-library/src/navigation/frontend.js
+++ b/packages/block-library/src/navigation/frontend.js
@@ -14,6 +14,10 @@ function navigationToggleModal( modal ) {
 	triggerButton.setAttribute( 'aria-expanded', ! isHidden );
 	closeButton.setAttribute( 'aria-expanded', ! isHidden );
 	modal.classList.toggle( 'has-modal-open', ! isHidden );
+
+	// Add a class to indicate the modal is open.
+	const htmlElement = document.querySelector( 'html' );
+	htmlElement.classList.toggle( 'has-modal-open' );
 }
 
 MicroModal.init( {