diff --git a/unix/x0vncserver/PollingManager.cxx b/unix/x0vncserver/PollingManager.cxx
index 9ae8d15..9140778 100644
--- a/unix/x0vncserver/PollingManager.cxx
+++ b/unix/x0vncserver/PollingManager.cxx
@@ -63,19 +63,14 @@
     m_offsetLeft(offsetLeft),
     m_offsetTop(offsetTop),
     m_width(image->xim->width),
-    m_height(m_image->xim->height),
+    m_height(image->xim->height),
+    m_widthTiles((image->xim->width + 31) / 32),
+    m_heightTiles((image->xim->height + 31) / 32),
+    m_numTiles(((image->xim->width + 31) / 32) *
+               ((image->xim->height + 31) / 32)),
     m_numVideoPasses(0),
     m_pollingStep(0)
 {
-  // Save width and height of the screen (and the image).
-  m_width = m_image->xim->width;
-  m_height = m_image->xim->height;
-
-  // Compute width and height in 32x32 tiles.
-  m_widthTiles = (m_width + 31) / 32;
-  m_heightTiles = (m_height + 31) / 32;
-  m_numTiles = m_widthTiles * m_heightTiles;
-
   // Get initial screen image.
   m_image->get(DefaultRootWindow(m_dpy), m_offsetLeft, m_offsetTop);
 
diff --git a/unix/x0vncserver/PollingManager.h b/unix/x0vncserver/PollingManager.h
index 25323b5..9f3ff88 100644
--- a/unix/x0vncserver/PollingManager.h
+++ b/unix/x0vncserver/PollingManager.h
@@ -64,12 +64,12 @@
   VNCServer *m_server;
 
   Image *m_image;
-  int m_bytesPerPixel;
+  const int m_bytesPerPixel;
 
-  int m_offsetLeft;
-  int m_offsetTop;
-  int m_width;
-  int m_height;
+  const int m_offsetLeft;
+  const int m_offsetTop;
+  const int m_width;
+  const int m_height;
 
 private:
 
@@ -120,9 +120,9 @@
   Image *m_rowImage;            // one row of the framebuffer
   Image *m_columnImage;         // one column of the framebuffer
 
-  int m_widthTiles;		// shortcut for ((m_width + 31) / 32)
-  int m_heightTiles;		// shortcut for ((m_height + 31) / 32)
-  int m_numTiles;		// shortcut for (m_widthTiles * m_heightTiles)
+  const int m_widthTiles;       // shortcut for ((m_width + 31) / 32)
+  const int m_heightTiles;      // shortcut for ((m_height + 31) / 32)
+  const int m_numTiles;         // shortcut for (m_widthTiles * m_heightTiles)
 
   // m_changeFlags[] array will hold boolean values corresponding to
   // each 32x32 tile. If a value is true, then we've detected a change