diff --git a/content/media/webaudio/AudioContext.cpp b/content/media/webaudio/AudioContext.cpp
index 68114e569e99..fb590b1fd682 100644
--- a/content/media/webaudio/AudioContext.cpp
+++ b/content/media/webaudio/AudioContext.cpp
@@ -59,6 +59,7 @@ AudioContext::AudioContext(nsPIDOMWindow* aWindow,
                                           aLength, aSampleRate))
   , mNumberOfChannels(aNumberOfChannels)
   , mIsOffline(aIsOffline)
+  , mIsStarted(!aIsOffline)
 {
   // Actually play audio
   mDestination->Stream()->AddAudioOutput(&gWebAudioOutputKey);
@@ -595,10 +596,15 @@ AudioContext::GetJSContext() const
 }
 
 void
-AudioContext::StartRendering()
+AudioContext::StartRendering(ErrorResult& aRv)
 {
   MOZ_ASSERT(mIsOffline, "This should only be called on OfflineAudioContext");
+  if (mIsStarted) {
+    aRv.Throw(NS_ERROR_DOM_INVALID_STATE_ERR);
+    return;
+  }
 
+  mIsStarted = true;
   mDestination->StartRendering();
 }
 
diff --git a/content/media/webaudio/AudioContext.h b/content/media/webaudio/AudioContext.h
index 19759604e339..69dd2c1ede9a 100644
--- a/content/media/webaudio/AudioContext.h
+++ b/content/media/webaudio/AudioContext.h
@@ -205,7 +205,7 @@ public:
                        const Optional<OwningNonNull<DecodeErrorCallback> >& aFailureCallback);
 
   // OfflineAudioContext methods
-  void StartRendering();
+  void StartRendering(ErrorResult& aRv);
   IMPL_EVENT_HANDLER(complete)
 
   bool IsOffline() const { return mIsOffline; }
@@ -251,6 +251,7 @@ private:
   // Number of channels passed in the OfflineAudioContext ctor.
   uint32_t mNumberOfChannels;
   bool mIsOffline;
+  bool mIsStarted;
 };
 
 }
diff --git a/content/media/webaudio/test/test_OfflineAudioContext.html b/content/media/webaudio/test/test_OfflineAudioContext.html
index 29c58edd80bc..3e0240f30fca 100644
--- a/content/media/webaudio/test/test_OfflineAudioContext.html
+++ b/content/media/webaudio/test/test_OfflineAudioContext.html
@@ -54,6 +54,10 @@ addLoadEvent(function() {
     compareBuffers(e.renderedBuffer.getChannelData(0), buf.getChannelData(0));
     compareBuffers(e.renderedBuffer.getChannelData(1), buf.getChannelData(1));
 
+    expectException(function() {
+      ctx.startRendering();
+    }, DOMException.INVALID_STATE_ERR);
+
     SimpleTest.finish();
   }, false);
 });
diff --git a/dom/webidl/OfflineAudioContext.webidl b/dom/webidl/OfflineAudioContext.webidl
index ee2ba3019d7e..1fa0d1cf87cd 100644
--- a/dom/webidl/OfflineAudioContext.webidl
+++ b/dom/webidl/OfflineAudioContext.webidl
@@ -1,4 +1,4 @@
-/* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* -*- Mode: IDL; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this file,
  * You can obtain one at http://mozilla.org/MPL/2.0/.
@@ -16,6 +16,7 @@ callback OfflineRenderSuccessCallback = void (AudioBuffer renderedData);
  PrefControlled]
 interface OfflineAudioContext : AudioContext {
 
+    [Throws]
     void startRendering();
 
     attribute EventHandler oncomplete;