diff --git a/xpcom/proxy/src/nsProxyEvent.cpp b/xpcom/proxy/src/nsProxyEvent.cpp
index aabb46d39dac..96616364ef51 100644
--- a/xpcom/proxy/src/nsProxyEvent.cpp
+++ b/xpcom/proxy/src/nsProxyEvent.cpp
@@ -49,7 +49,7 @@ nsProxyObjectCallInfo::~nsProxyObjectCallInfo()
         free( (void*) mParameterList);
 }
 
-
+static NS_DEFINE_IID(kISupportsIID, NS_ISUPPORTS_IID);
 NS_IMPL_ISUPPORTS(nsProxyObject, kISupportsIID)
 
 static NS_DEFINE_IID(kIEventQIID, NS_IEVENTQUEUE_IID);