diff --git a/src/source/source_cache.js b/src/source/source_cache.js
index a8b5af3b597..ed2f3e8ac9e 100644
--- a/src/source/source_cache.js
+++ b/src/source/source_cache.js
@@ -708,7 +708,7 @@ class SourceCache extends Evented {
         if (tile.uses > 0)
             return;
 
-        if (tile.hasData()) {
+        if (tile.hasData() && tile.state !== 'reloading') {
             this._cache.add(tile.tileID, tile, tile.getExpiryTimeout());
         } else {
             tile.aborted = true;
diff --git a/src/util/dispatcher.js b/src/util/dispatcher.js
index bb43c1d1864..2b4fb9d112a 100644
--- a/src/util/dispatcher.js
+++ b/src/util/dispatcher.js
@@ -2,6 +2,7 @@
 
 import { uniqueId, asyncAll } from './util';
 import Actor from './actor';
+import assert from 'assert';
 
 import type WorkerPool from './worker_pool';
 
@@ -32,12 +33,14 @@ class Dispatcher {
             actor.name = `Worker ${i}`;
             this.actors.push(actor);
         }
+        assert(this.actors.length);
     }
 
     /**
      * Broadcast a message to all Workers.
      */
     broadcast(type: string, data: mixed, cb?: Function) {
+        assert(this.actors.length);
         cb = cb || function () {};
         asyncAll(this.actors, (actor, done) => {
             actor.send(type, data, done);
@@ -49,6 +52,7 @@ class Dispatcher {
      * @returns An actor object backed by a web worker for processing messages.
      */
     getActor(): Actor {
+        assert(this.actors.length);
         this.currentActor = (this.currentActor + 1) % this.actors.length;
         return this.actors[this.currentActor];
     }