#define PANEL_FB_WIDTH_OFFSET_MASK                    0x3fff
 
 #define PANEL_WINDOW_WIDTH                            0x080014
-#define PANEL_WINDOW_WIDTH_WIDTH                      27:16
-#define PANEL_WINDOW_WIDTH_X                          11:0
+#define PANEL_WINDOW_WIDTH_WIDTH_SHIFT                16
+#define PANEL_WINDOW_WIDTH_WIDTH_MASK                 (0xfff << 16)
+#define PANEL_WINDOW_WIDTH_X_MASK                     0xfff
 
 #define PANEL_WINDOW_HEIGHT                           0x080018
 #define PANEL_WINDOW_HEIGHT_HEIGHT                    27:16
 
                reg |= (fix->line_length & PANEL_FB_WIDTH_OFFSET_MASK);
                POKE32(PANEL_FB_WIDTH, reg);
 
-               POKE32(PANEL_WINDOW_WIDTH,
-                       FIELD_VALUE(0, PANEL_WINDOW_WIDTH, WIDTH, var->xres - 1)|
-                       FIELD_VALUE(0, PANEL_WINDOW_WIDTH, X, var->xoffset));
+               reg = ((var->xres - 1) << PANEL_WINDOW_WIDTH_WIDTH_SHIFT) &
+                      PANEL_WINDOW_WIDTH_WIDTH_MASK;
+               reg |= (var->xoffset & PANEL_WINDOW_WIDTH_X_MASK);
+               POKE32(PANEL_WINDOW_WIDTH, reg);
 
                POKE32(PANEL_WINDOW_HEIGHT,
                        FIELD_VALUE(0, PANEL_WINDOW_HEIGHT, HEIGHT, var->yres_virtual - 1)|