diff --git a/karma.conf.js b/karma.conf.js
index 18f743dee6..5025dc4d54 100644
--- a/karma.conf.js
+++ b/karma.conf.js
@@ -38,8 +38,8 @@ module.exports = function(config) {
       '/assets/': '/base/assets/'
     },
 
-    // do not panic about "no activity" unless a test takes longer than 60s.
-    browserNoActivityTimeout: 60000,
+    // do not panic about "no activity" unless a test takes longer than 70s.
+    browserNoActivityTimeout: 70000,
 
     // don't capture the client's console logs
     client: { captureConsole: false },
diff --git a/lib/media/source_buffer_manager.js b/lib/media/source_buffer_manager.js
index a33e160420..f886792a3d 100644
--- a/lib/media/source_buffer_manager.js
+++ b/lib/media/source_buffer_manager.js
@@ -627,11 +627,13 @@ shaka.media.SourceBufferManager.prototype.clearAfter_ = function(timestamp) {
  */
 shaka.media.SourceBufferManager.prototype.abort_ = function() {
   shaka.log.v1(this.logPrefix_(), 'abort_');
-  shaka.asserts.assert(this.operationPromise_);
-
-  // See {@link http://www.w3.org/TR/media-source/#widl-SourceBuffer-abort-void}
-  if (this.mediaSource_.readyState == 'open') {
-    this.sourceBuffer_.abort();
+  // Due to a race caused by Promise polyfills, operationPromise_ might be null
+  // when abort_ is called.  In this case, the operation is already aborted.
+  if (this.operationPromise_) {
+    // See http://www.w3.org/TR/media-source/#widl-SourceBuffer-abort-void
+    if (this.mediaSource_.readyState == 'open') {
+      this.sourceBuffer_.abort();
+    }
   }
 };
 
diff --git a/spec/task_spec.js b/spec/task_spec.js
index b2b2ea0012..e1bb943a0c 100644
--- a/spec/task_spec.js
+++ b/spec/task_spec.js
@@ -125,30 +125,30 @@ describe('Task', function() {
 
       setTimeout(function() {
         expect(stages).toEqual([0]);
-      }, 10);
+      }, 15);
       setTimeout(function() {
         expect(stages).toEqual([0]);
         p0.resolve();
-      }, 20);
+      }, 30);
 
       setTimeout(function() {
         expect(stages).toEqual([0, 1]);
-      }, 30);
+      }, 45);
       setTimeout(function() {
         expect(stages).toEqual([0, 1]);
         p1.resolve();
-      }, 40);
+      }, 60);
 
       setTimeout(function() {
         expect(stages).toEqual([0, 1, 2]);
         // We've run the final stage, but it's not done until p2 is resolved.
         expect(complete).toBe(false);
-      }, 50);
+      }, 75);
       setTimeout(function() {
         expect(stages).toEqual([0, 1, 2]);
         expect(complete).toBe(false);
         p2.resolve();
-      }, 60);
+      }, 90);
 
       t.getPromise().then(function() {
         complete = true;