diff --git a/content/base/src/nsDocument.h b/content/base/src/nsDocument.h
index 3ff0553b784..f2d852efcc4 100644
--- a/content/base/src/nsDocument.h
+++ b/content/base/src/nsDocument.h
@@ -42,7 +42,7 @@
 #include "nsWeakReference.h"
 #include "nsWeakPtr.h"
 #include "nsVoidArray.h"
-#include "nsIDOMDocument.h"
+#include "nsIDOMXMLDocument.h"
 #include "nsIDOMDocumentView.h"
 #include "nsIDOMDocumentXBL.h"
 #include "nsIDOMNSDocument.h"
@@ -212,9 +212,17 @@ protected:
   void*         mScriptObject;
 };
 
-// Base class for our document implementations
+// Base class for our document implementations.
+//
+// Note that this class *implements* nsIDOMXMLDocument, but it's not
+// really an nsIDOMXMLDocument. The reason for implementing
+// nsIDOMXMLDocument on this class is to avoid having to duplicate all
+// its inherited methods on document classes that *are*
+// nsIDOMXMLDocument's. nsDocument's QI should *not* claim to support
+// nsIDOMXMLDocument unless someone writes a real implementation of
+// the interface.
 class nsDocument : public nsIDocument, 
-                   public nsIDOMDocument, 
+                   public nsIDOMXMLDocument, // inherits nsIDOMDocument 
                    public nsIDOMNSDocument,
                    public nsIDOMDocumentEvent,
                    public nsIDOMDocumentStyle,
@@ -489,6 +497,9 @@ public:
   // nsIDOMDocument
   NS_DECL_NSIDOMDOCUMENT
 
+  // nsIDOMXMLDocument
+  NS_DECL_NSIDOMXMLDOCUMENT
+
   // nsIDOMNSDocument
   NS_DECL_NSIDOMNSDOCUMENT
 
diff --git a/content/xml/document/src/nsXMLDocument.h b/content/xml/document/src/nsXMLDocument.h
index 3867b2f61b8..7e4748adeeb 100644
--- a/content/xml/document/src/nsXMLDocument.h
+++ b/content/xml/document/src/nsXMLDocument.h
@@ -56,8 +56,7 @@ class nsXMLDocument : public nsMarkupDocument,
                       public nsIXMLDocument,
                       public nsIHTMLContentContainer,
                       public nsIInterfaceRequestor,
-                      public nsIHttpEventSink,
-                      public nsIDOMXMLDocument
+                      public nsIHttpEventSink
 {
 public:
   nsXMLDocument();
diff --git a/dom/public/idl/core/nsIDOMXMLDocument.idl b/dom/public/idl/core/nsIDOMXMLDocument.idl
index b92dddec1e5..adcdc2894a6 100644
--- a/dom/public/idl/core/nsIDOMXMLDocument.idl
+++ b/dom/public/idl/core/nsIDOMXMLDocument.idl
@@ -37,10 +37,10 @@
  *
  * ***** END LICENSE BLOCK ***** */
 
-#include "domstubs.idl"
+#include "nsIDOMDocument.idl"
 
 [scriptable, uuid(8816d003-e7c8-4065-8827-829b8d07b6e0)]
-interface nsIDOMXMLDocument : nsISupports
+interface nsIDOMXMLDocument : nsIDOMDocument
 {
   void                      load(in DOMString url);
 };
diff --git a/dom/src/base/nsDOMClassInfo.cpp b/dom/src/base/nsDOMClassInfo.cpp
index 651d0af83bf..e87aea59a04 100644
--- a/dom/src/base/nsDOMClassInfo.cpp
+++ b/dom/src/base/nsDOMClassInfo.cpp
@@ -987,7 +987,7 @@ nsDOMClassInfo::Init()
     DOM_CLASSINFO_MAP_ENTRY(nsIDOMScreen)
   DOM_CLASSINFO_MAP_END
 
-  DOM_CLASSINFO_MAP_BEGIN(XMLDocument, nsIDOMDocument)
+  DOM_CLASSINFO_MAP_BEGIN(XMLDocument, nsIDOMXMLDocument)
     DOM_CLASSINFO_MAP_ENTRY(nsIDOMDocument)
     DOM_CLASSINFO_MAP_ENTRY(nsIDOMXMLDocument)
     DOM_CLASSINFO_MAP_ENTRY(nsIDOMNSDocument)