diff --git a/src/material/list/list.ts b/src/material/list/list.ts
index 583f10f1bff7..642064c411dc 100644
--- a/src/material/list/list.ts
+++ b/src/material/list/list.ts
@@ -74,7 +74,7 @@ export class MatListItem extends MatListItemBase {
 
   /** Indicates whether an item in a `<mat-nav-list>` is the currently active page. */
   @Input()
-  get activated() {
+  get activated(): boolean {
     return this._activated;
   }
   set activated(activated) {