diff --git a/unix/x0vncserver/PollingManager.h b/unix/x0vncserver/PollingManager.h
index 19a743e..9d62f0b 100644
--- a/unix/x0vncserver/PollingManager.h
+++ b/unix/x0vncserver/PollingManager.h
@@ -98,10 +98,14 @@
   }
 
   int checkRow(int x, int y, int w, bool *pChangeFlags);
+  int checkColumn(int x, int y, int h, bool *pChangeFlags);
   void sendChanges(const bool *pChangeFlags);
   void handleVideo(const bool *pChangeFlags);
   void flagVideoArea(bool *pChangeFlags, bool value);
 
+  // Check neighboring tiles and update pmxChanged[] matrix.
+  void checkNeighbors(bool *pChangeFlags);
+
   // Video detection functions.
   void detectVideo();
   void getVideoAreaRect(Rect *result);