diff --git a/packages/edit-site/src/components/sidebar-navigation-screen-patterns/use-template-part-areas.js b/packages/edit-site/src/components/sidebar-navigation-screen-patterns/use-template-part-areas.js
index 77cbf87b3d439..57d1aeaaabbd6 100644
--- a/packages/edit-site/src/components/sidebar-navigation-screen-patterns/use-template-part-areas.js
+++ b/packages/edit-site/src/components/sidebar-navigation-screen-patterns/use-template-part-areas.js
@@ -43,7 +43,7 @@ const useTemplatePartsGroupedByArea = ( items ) => {
 		const key = accumulator[ item.area ]
 			? item.area
 			: TEMPLATE_PART_AREA_DEFAULT_CATEGORY;
-		accumulator[ key ].templateParts.push( item );
+		accumulator[ key ]?.templateParts?.push( item );
 		return accumulator;
 	}, knownAreas );