diff --git a/mozilla/netwerk/protocol/res/src/nsResProtocolHandler.cpp b/mozilla/netwerk/protocol/res/src/nsResProtocolHandler.cpp
index 907d775f30d..7959bb1ab41 100644
--- a/mozilla/netwerk/protocol/res/src/nsResProtocolHandler.cpp
+++ b/mozilla/netwerk/protocol/res/src/nsResProtocolHandler.cpp
@@ -51,6 +51,7 @@
 #include "nsDirectoryServiceDefs.h"
 #include "nsNetUtil.h"
 #include "nsURLHelper.h"
+#include "nsEscape.h"
 
 static NS_DEFINE_CID(kResURLCID, NS_RESURL_CID);
 
@@ -332,6 +333,10 @@ nsResProtocolHandler::ResolveURI(nsIURI *uri, nsACString &result)
     if (filepath.FindChar(':') != -1)
         return NS_ERROR_MALFORMED_URI;
 
+    NS_UnescapeURL(filepath);
+    if (filepath.FindChar('\\') != -1)
+        return NS_ERROR_MALFORMED_URI;
+
     const char *p = path.get() + 1; // path always starts with a slash
     NS_ASSERTION(*(p-1) == '/', "Path did not begin with a slash!");