diff --git a/unix/x0vncserver/PollingManager.h b/unix/x0vncserver/PollingManager.h
index 2ed9ff5..e106f79 100644
--- a/unix/x0vncserver/PollingManager.h
+++ b/unix/x0vncserver/PollingManager.h
@@ -85,7 +85,7 @@
 
   int checkRow(int x, int y, int w);
   int checkColumn(int x, int y, int h, bool *pChangeFlags);
-  int sendChanges(VNCServer *server);
+  int sendChanges(VNCServer *server) const;
 
   // Check neighboring tiles and update m_changeFlags[].
   void checkNeighbors();