diff --git a/unix/x0vncserver/PollingManager.cxx b/unix/x0vncserver/PollingManager.cxx
index 81624a9..a1534d9 100644
--- a/unix/x0vncserver/PollingManager.cxx
+++ b/unix/x0vncserver/PollingManager.cxx
@@ -255,7 +255,7 @@
   return nTilesChanged;
 }
 
-int PollingManager::sendChanges(VNCServer *server)
+int PollingManager::sendChanges(VNCServer *server) const
 {
   const bool *pChangeFlags = m_changeFlags;
   int nTilesChanged = 0;
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();