diff --git a/netwerk/base/public/nsIChannel.idl b/netwerk/base/public/nsIChannel.idl
index 32f21d39122..ccf02a7d8ee 100644
--- a/netwerk/base/public/nsIChannel.idl
+++ b/netwerk/base/public/nsIChannel.idl
@@ -56,7 +56,7 @@ interface nsIStreamListener;
  *
  * This interface must be used only from the XPCOM main thread.
  */
-[scriptable, uuid(e0bb5c49-c54e-4efb-8f0d-6a7edd926fab)]
+[scriptable, uuid(c63a055a-a676-4e71-bf3c-6cfa11082018)]
 interface nsIChannel : nsIRequest
 {
     /**
@@ -151,11 +151,13 @@ interface nsIChannel : nsIRequest
 
     /**
      * The length of the data associated with the channel if available.  A value
-     * of -1 indicates that the content length is unknown. Note that this
-     * is a 64-bit value and obsoletes the "content-length" property used on
-     * some channels.
+     * of -1 indicates that the content length is unknown.
+     *
+     * Callers should prefer getting the "content-length" property
+     * as 64-bit value by QIing the channel to nsIPropertyBag2,
+     * if that interface is exposed by the channel.
      */
-    attribute PRInt64 contentLength;
+    attribute long contentLength;
 
     /**
      * Synchronously open the channel.