--- a/dom/media/webaudio/ScriptProcessorNode.cpp
+++ b/dom/media/webaudio/ScriptProcessorNode.cpp
@@ -240,30 +240,24 @@ private:
 class ScriptProcessorNodeEngine final : public AudioNodeEngine
 {
 public:
   ScriptProcessorNodeEngine(ScriptProcessorNode* aNode,
                             AudioDestinationNode* aDestination,
                             uint32_t aBufferSize,
                             uint32_t aNumberOfInputChannels)
     : AudioNodeEngine(aNode)
-    , mSource(nullptr)
     , mDestination(aDestination->Stream())
+    , mSharedBuffers(new SharedBuffers(mDestination->SampleRate()))
     , mBufferSize(aBufferSize)
     , mInputChannelCount(aNumberOfInputChannels)
     , mInputWriteIndex(0)
   {
   }
 
-  void SetSourceStream(AudioNodeStream* aSource)
-  {
-    mSource = aSource;
-    mSharedBuffers = new SharedBuffers(mSource->SampleRate());
-  }
-
   SharedBuffers* GetSharedBuffers() const
   {
     return mSharedBuffers;
   }
 
   enum {
     IS_CONNECTED,
   };
@@ -340,17 +334,16 @@ public:
     // by main thread events calling
     // SharedBuffers::FinishProducingOutputBuffer() have been processed.
     return true;
   }
 
   virtual size_t SizeOfExcludingThis(MallocSizeOf aMallocSizeOf) const override
   {
     // Not owned:
-    // - mSource (probably)
     // - mDestination (probably)
     size_t amount = AudioNodeEngine::SizeOfExcludingThis(aMallocSizeOf);
     amount += mSharedBuffers->SizeOfIncludingThis(aMallocSizeOf);
     amount += mInputBuffer->SizeOfIncludingThis(aMallocSizeOf);
 
     return amount;
   }
 
@@ -472,19 +465,18 @@ private:
     };
 
     NS_DispatchToMainThread(new Command(aStream, mInputBuffer.forget(),
                                         playbackTime));
   }
 
   friend class ScriptProcessorNode;
 
+  AudioNodeStream* mDestination;
   nsAutoPtr<SharedBuffers> mSharedBuffers;
-  AudioNodeStream* mSource;
-  AudioNodeStream* mDestination;
   nsRefPtr<ThreadSharedFloatArrayBufferList> mInputBuffer;
   const uint32_t mBufferSize;
   const uint32_t mInputChannelCount;
   // The write index into the current input buffer
   uint32_t mInputWriteIndex;
   bool mIsConnected = false;
 };
 
@@ -504,17 +496,16 @@ ScriptProcessorNode::ScriptProcessorNode
   MOZ_ASSERT(BufferSize() % WEBAUDIO_BLOCK_SIZE == 0, "Invalid buffer size");
   ScriptProcessorNodeEngine* engine =
     new ScriptProcessorNodeEngine(this,
                                   aContext->Destination(),
                                   BufferSize(),
                                   aNumberOfInputChannels);
   mStream = AudioNodeStream::Create(aContext, engine,
                                     AudioNodeStream::NO_STREAM_FLAGS);
-  engine->SetSourceStream(mStream);
 }
 
 ScriptProcessorNode::~ScriptProcessorNode()
 {
 }
 
 size_t
 ScriptProcessorNode::SizeOfExcludingThis(MallocSizeOf aMallocSizeOf) const