diff --git a/GameRes/GameRes.cs b/GameRes/GameRes.cs
index 392f6f05..e1a9e602 100644
--- a/GameRes/GameRes.cs
+++ b/GameRes/GameRes.cs
@@ -95,10 +95,19 @@ namespace GameRes
 
         protected IResource ()
         {
-            Extensions = new string[] { Tag.ToLowerInvariant() };
+            Extensions = new string[] { GetDefaultExtension() };
             Signatures = new uint[] { this.Signature };
         }
 
+        protected string GetDefaultExtension ()
+        {
+            var ext = Tag.ToLowerInvariant();
+            int slash = ext.IndexOf ('/');
+            if (slash != -1)
+                ext = ext.Substring (0, slash);
+            return ext;
+        }
+
         public virtual ResourceOptions GetDefaultOptions ()
         {
             return null;