diff --git a/mw/Map.d.ts b/mw/Map.d.ts
index a14e25f..adfb0c3 100644
--- a/mw/Map.d.ts
+++ b/mw/Map.d.ts
@@ -27,7 +27,7 @@ declare global {
              * @returns True if the key exists
              * @see https://doc.wikimedia.org/mediawiki-core/master/js/#!/api/mw.Map-method-exists
              */
-            exists(selection: keyof V): boolean;
+            exists<S extends keyof V>(selection: S): selection is S;
 
             /**
              * Get the value of one or more keys.
@@ -53,7 +53,7 @@ declare global {
              * @see https://doc.wikimedia.org/mediawiki-core/master/js/#!/api/mw.Map-method-set
              */
             set<S extends keyof V>(selection: S, value: V[S]): boolean;
-            set(selection: Partial<V>): boolean;
+            set<S extends Partial<V>>(selection: S): boolean;
         }
     }
 }