diff --git a/dom/media/webaudio/FFTBlock.h b/dom/media/webaudio/FFTBlock.h
index 44f1e7a57c8..cefa92e3636 100644
--- a/dom/media/webaudio/FFTBlock.h
+++ b/dom/media/webaudio/FFTBlock.h
@@ -217,10 +217,18 @@ public:
   {
     return mOutputBuffer[aIndex].r;
   }
+  float& RealData(uint32_t aIndex)
+  {
+    return mOutputBuffer[aIndex].r;
+  }
   float ImagData(uint32_t aIndex) const
   {
     return mOutputBuffer[aIndex].i;
   }
+  float& ImagData(uint32_t aIndex)
+  {
+    return mOutputBuffer[aIndex].i;
+  }
 
   size_t SizeOfExcludingThis(MallocSizeOf aMallocSizeOf) const
   {