diff --git a/mozilla/netwerk/protocol/file/src/nsFileProtocolHandler.cpp b/mozilla/netwerk/protocol/file/src/nsFileProtocolHandler.cpp
index 5f732ccd8c5..b73b2ae04ce 100644
--- a/mozilla/netwerk/protocol/file/src/nsFileProtocolHandler.cpp
+++ b/mozilla/netwerk/protocol/file/src/nsFileProtocolHandler.cpp
@@ -248,6 +248,7 @@ nsFileProtocolHandler::NewFileURI(nsIFile *file, nsIURI **result)
 NS_IMETHODIMP
 nsFileProtocolHandler::GetURLSpecFromFile(nsIFile *file, nsACString &result)
 {
+    NS_ENSURE_ARG_POINTER(file);
     return net_GetURLSpecFromFile(file, result);
 }