diff --git a/io.h b/io.h
index d811f6ea2..b7abbec76 100644
--- a/io.h
+++ b/io.h
@@ -108,7 +108,7 @@ public:
     {
     }
 
-    ~io_data_t()
+    virtual ~io_data_t()
     {
         free((void *)filename_cstr);
     }