diff --git a/dom/media/webaudio/AudioBuffer.cpp b/dom/media/webaudio/AudioBuffer.cpp
index e7eba2d48..e4252dfcf 100644
--- a/dom/media/webaudio/AudioBuffer.cpp
+++ b/dom/media/webaudio/AudioBuffer.cpp
@@ -254,8 +254,6 @@ void
 AudioBuffer::CopyFromChannel(const Float32Array& aDestination, uint32_t aChannelNumber,
                              uint32_t aStartInChannel, ErrorResult& aRv)
 {
-  aDestination.ComputeLengthAndData();
-
   uint32_t length = aDestination.Length();
   CheckedInt<uint32_t> end = aStartInChannel;
   end += length;
@@ -266,6 +264,7 @@ AudioBuffer::CopyFromChannel(const Float32Array& aDestination, uint32_t aChannel
   }
 
   JS::AutoCheckCannotGC nogc;
+  aDestination.ComputeLengthAndData();
   JSObject* channelArray = mJSChannels[aChannelNumber];
   const float* sourceData = nullptr;
   if (channelArray) {
@@ -296,8 +295,6 @@ AudioBuffer::CopyToChannel(JSContext* aJSContext, const Float32Array& aSource,
                            uint32_t aChannelNumber, uint32_t aStartInChannel,
                            ErrorResult& aRv)
 {
-  aSource.ComputeLengthAndData();
-
   uint32_t length = aSource.Length();
   CheckedInt<uint32_t> end = aStartInChannel;
   end += length;
@@ -320,6 +317,7 @@ AudioBuffer::CopyToChannel(JSContext* aJSContext, const Float32Array& aSource,
     return;
   }
 
+  aSource.ComputeLengthAndData();
   bool isShared = false;
   float* channelData = JS_GetFloat32ArrayData(channelArray, &isShared, nogc);
   // The channelData arrays should all have originated in