diff --git a/modules/libpr0n/decoders/icon/nsIconURI.cpp b/modules/libpr0n/decoders/icon/nsIconURI.cpp
index 3004c5e6e5b..c50d1d1ece5 100644
--- a/modules/libpr0n/decoders/icon/nsIconURI.cpp
+++ b/modules/libpr0n/decoders/icon/nsIconURI.cpp
@@ -44,7 +44,7 @@ nsMozIconURI::~nsMozIconURI()
 {
 }
 
-NS_IMPL_THREADSAFE_ISUPPORTS3(nsMozIconURI, nsIMozIconURI, nsIURI, nsISerializable)
+NS_IMPL_THREADSAFE_ISUPPORTS2(nsMozIconURI, nsIMozIconURI, nsIURI)
 
 #define NS_MOZICON_SCHEME           "moz-icon:"
 #define NS_MOZ_ICON_DELIMITER        '?'