diff --git a/src/source/source_cache.js b/src/source/source_cache.js
index 757b76c02cf..679423aa16f 100644
--- a/src/source/source_cache.js
+++ b/src/source/source_cache.js
@@ -650,10 +650,10 @@ class SourceCache extends Evented {
     _updateLoadedParentTileCache() {
         this._loadedParentTiles = {};
 
-        for (const tile of (Object.values(this._tiles): any)) {
+        for (const tileKey in this._tiles) {
             const path = [];
             let parentTile: ?Tile;
-            let currentId = tile.tileID;
+            let currentId = this._tiles[tileKey].tileID;
 
             // Find the closest loaded ancestor by traversing the tile tree towards the root and
             // caching results along the way
@@ -678,8 +678,8 @@ class SourceCache extends Evented {
             }
 
             // Cache the result of this traversal to all newly visited tiles
-            for (let i = 0; i < path.length; i++) {
-                this._loadedParentTiles[path[i]] = parentTile;
+            for (const key of path) {
+                this._loadedParentTiles[key] = parentTile;
             }
         }
     }