--- a/xpinstall/src/nsXPInstallManager.cpp
+++ b/xpinstall/src/nsXPInstallManager.cpp
@@ -123,16 +123,17 @@ NS_INTERFACE_MAP_BEGIN(nsXPInstallManage
   NS_INTERFACE_MAP_ENTRY(nsIObserver)
   NS_INTERFACE_MAP_ENTRY(nsIStreamListener)
   NS_INTERFACE_MAP_ENTRY(nsIProgressEventSink)
   NS_INTERFACE_MAP_ENTRY(nsIInterfaceRequestor)
   NS_INTERFACE_MAP_ENTRY(nsPICertNotification)
   NS_INTERFACE_MAP_ENTRY(nsIBadCertListener2)
   NS_INTERFACE_MAP_ENTRY(nsISSLErrorListener)
   NS_INTERFACE_MAP_ENTRY(nsIChannelEventSink)
+  NS_INTERFACE_MAP_ENTRY(nsISupportsWeakReference)
   NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, nsISupportsWeakReference)
 NS_INTERFACE_MAP_END
 
 NS_IMPL_ADDREF(nsXPInstallManager)
 NS_IMPL_RELEASE(nsXPInstallManager)
 
 NS_IMETHODIMP
 nsXPInstallManager::InitManagerFromChrome(const PRUnichar **aURLs,