diff --git a/src/app.ts b/src/app.ts
index 37aae93..acd255a 100644
--- a/src/app.ts
+++ b/src/app.ts
@@ -29,7 +29,7 @@ window.onload = () => {
 
         xhr.onload = function() {
                 var mapDef = new MapData(JSON.parse(this.responseText));
-                var inputHandler = new InputHandler(util.numberArrayToMap(relevantKeys));
+                var inputHandler = new InputHandler(util.arrayToObject(relevantKeys));
                 mapContext = new MapContext(mapDef, inputHandler);
         }
 
diff --git a/src/util.ts b/src/util.ts
index ad2b482..0761d2d 100644
--- a/src/util.ts
+++ b/src/util.ts
@@ -12,8 +12,8 @@ export function mapPromises<T>(promises: {[key: string]: Promise<T>}): Promise<{
         return Promise.all(p).then(() => ret);
 }
 
-export function numberArrayToMap(arr: number[]): {[key: number]: boolean} {
-        var ret: {[key: number]: boolean} = {};
+export function arrayToObject(arr: (number|string)[]): {[key: string]: boolean} {
+        var ret: {[key: string]: boolean} = {};
 
         for (let v of arr)
                 ret[v] = true;