diff --git a/mert/FileStream.h b/mert/FileStream.h
index cdf786632..78b6ccb88 100644
--- a/mert/FileStream.h
+++ b/mert/FileStream.h
@@ -13,7 +13,8 @@ protected:
 
 public:
   explicit inputfilestream(const std::string &filePath);
-  ~inputfilestream();
+  virtual ~inputfilestream();
+
   bool good() const { return is_good; }
   void close();
 };
@@ -26,7 +27,8 @@ protected:
 
 public:
   explicit outputfilestream(const std::string &filePath);
-  ~outputfilestream();
+  virtual ~outputfilestream();
+
   bool good() const { return is_good; }
   void close();
 };
diff --git a/mert/gzfilebuf.h b/mert/gzfilebuf.h
index 3a5ef90dd..b0f9637b3 100644
--- a/mert/gzfilebuf.h
+++ b/mert/gzfilebuf.h
@@ -14,9 +14,11 @@ public:
           _buff+sizeof(int),     // read position
           _buff+sizeof(int));    // end position
   }
-  ~gzfilebuf() {
+
+  virtual ~gzfilebuf() {
     gzclose(_gzf);
   }
+
 protected:
   virtual int_type overflow (int_type c) {
     throw;