diff --git a/dom/media/webaudio/AudioBuffer.h b/dom/media/webaudio/AudioBuffer.h
index 921a0116de4d..e4280f090ccd 100644
--- a/dom/media/webaudio/AudioBuffer.h
+++ b/dom/media/webaudio/AudioBuffer.h
@@ -70,7 +70,7 @@ public:
     return mSampleRate;
   }
 
-  int32_t Length() const
+  uint32_t Length() const
   {
     return mLength;
   }
diff --git a/dom/webidl/AudioBuffer.webidl b/dom/webidl/AudioBuffer.webidl
index cb91e6292ba5..119daa7e2cab 100644
--- a/dom/webidl/AudioBuffer.webidl
+++ b/dom/webidl/AudioBuffer.webidl
@@ -13,12 +13,12 @@
 interface AudioBuffer {
 
     readonly attribute float sampleRate;
-    readonly attribute long length;
+    readonly attribute unsigned long length;
 
     // in seconds 
     readonly attribute double duration;
 
-    readonly attribute long numberOfChannels;
+    readonly attribute unsigned long numberOfChannels;
 
     [Throws]
     Float32Array getChannelData(unsigned long channel);