diff --git a/core/system.c b/core/system.c
index b718bb2..53a730b 100644
--- a/core/system.c
+++ b/core/system.c
@@ -404,11 +404,23 @@ void system_frame_gen(int do_skip)
     /* active screen height */
     if (reg[1] & 0x04)
     {
-      bitmap.viewport.h = 224 + ((reg[1] & 0x08) << 1);
-      bitmap.viewport.y = (config.overscan & 1) * ((240 + 48*vdp_pal - bitmap.viewport.h) >> 1);
+      /* Mode 5 */
+      if (reg[1] & 0x08)
+      {
+        /* 240 active lines */
+        bitmap.viewport.h = 240;
+        bitmap.viewport.y = (config.overscan & 1) * 24 * vdp_pal;
+      }
+      else
+      {
+        /* 224 active lines */
+        bitmap.viewport.h = 224;
+        bitmap.viewport.y = (config.overscan & 1) * (8 + (24 * vdp_pal));
+      }
     }
     else
     {
+      /* Mode 4 (192 active lines) */
       bitmap.viewport.h = 192;
       bitmap.viewport.y = (config.overscan & 1) * 24 * (vdp_pal + 1);
     }
diff --git a/core/vdp_ctrl.c b/core/vdp_ctrl.c
index f8f2d67..0f2ed16 100644
--- a/core/vdp_ctrl.c
+++ b/core/vdp_ctrl.c
@@ -1659,17 +1659,8 @@ static void vdp_reg_w(unsigned int r, unsigned int d, unsigned int cycles)
           /* Mode 5 only */
           if (d & 0x04)
           {
-            if (status & 8)
-            {
-              /* Changes should be applied on next frame */
-              bitmap.viewport.changed |= 2;
-            }
-            else
-            {
-              /* Update active display height */
-              bitmap.viewport.h = 224 + ((d & 8) << 1);
-              bitmap.viewport.y = (config.overscan & 1) * (8 - (d & 8) + 24*vdp_pal);
-            }
+            /* Changes should be applied on next frame */
+            bitmap.viewport.changed |= 2;
 
             /* Update vertical counter max value */
             vc_max = vc_table[(d >> 2) & 3][vdp_pal];