diff --git a/content/xul/document/public/xulstubs.idl b/content/xul/document/public/xulstubs.idl
index 598574934c94..86528ba8ef2b 100644
--- a/content/xul/document/public/xulstubs.idl
+++ b/content/xul/document/public/xulstubs.idl
@@ -33,6 +33,6 @@ interface nsIDOMXULElement : nsIDOMElement {};
 [scriptable, uuid(a6cf90ec-15b3-11d2-932e-00805f8add32)]
 interface nsIDOMXULTreeElement : nsIDOMXULElement {};
 
-%{
+%{C++
 #endif
 %}
diff --git a/rdf/base/idl/xulstubs.idl b/rdf/base/idl/xulstubs.idl
index 598574934c94..86528ba8ef2b 100644
--- a/rdf/base/idl/xulstubs.idl
+++ b/rdf/base/idl/xulstubs.idl
@@ -33,6 +33,6 @@ interface nsIDOMXULElement : nsIDOMElement {};
 [scriptable, uuid(a6cf90ec-15b3-11d2-932e-00805f8add32)]
 interface nsIDOMXULTreeElement : nsIDOMXULElement {};
 
-%{
+%{C++
 #endif
 %}