diff --git a/src/vid_oti067.c b/src/vid_oti067.c
index 7ae5a8d..1b7c20d 100644
--- a/src/vid_oti067.c
+++ b/src/vid_oti067.c
@@ -38,9 +38,11 @@ void oti067_out(uint16_t addr, uint8_t val, void *p)
         switch (addr)
         {
                 case 0x3D4:
-                svga->crtcreg = val & 31;
+                svga->crtcreg = val & 0x3f;
                 return;
                 case 0x3D5:
+                if (svga->crtcreg & 0x20)
+                        return;
                 if ((svga->crtcreg < 7) && (svga->crtc[0x11] & 0x80))
                         return;
                 if ((svga->crtcreg == 7) && (svga->crtc[0x11] & 0x80))
@@ -99,7 +101,10 @@ uint8_t oti067_in(uint16_t addr, void *p)
                 temp = svga->crtcreg;
                 break;
                 case 0x3D5:
-                temp = svga->crtc[svga->crtcreg];
+                if (svga->crtcreg & 0x20)
+                        temp = 0xff;
+                else
+                        temp = svga->crtc[svga->crtcreg];
                 break;
                 
                 case 0x3DE: 
diff --git a/src/vid_paradise.c b/src/vid_paradise.c
index b42482d..3aabd3a 100644
--- a/src/vid_paradise.c
+++ b/src/vid_paradise.c
@@ -110,12 +110,11 @@ void paradise_out(uint16_t addr, uint8_t val, void *p)
                 break;
                 
                 case 0x3D4:
-                if (paradise->type == PVGA1A)
-                   svga->crtcreg = val & 0x1f;
-                else
-                   svga->crtcreg = val & 0x3f;
+                svga->crtcreg = val & 0x3f;
                 return;
                 case 0x3D5:
+                if ((paradise->type == PVGA1A) && (svga->crtcreg & 0x20))
+                        return;
                 if ((svga->crtcreg < 7) && (svga->crtc[0x11] & 0x80))
                         return;
                 if ((svga->crtcreg == 7) && (svga->crtc[0x11] & 0x80))
@@ -191,6 +190,8 @@ uint8_t paradise_in(uint16_t addr, void *p)
                 case 0x3D4:
                 return svga->crtcreg;
                 case 0x3D5:
+                if ((paradise->type == PVGA1A) && (svga->crtcreg & 0x20))
+                        return 0xff;
                 if (svga->crtcreg > 0x29 && svga->crtcreg < 0x30 && (svga->crtc[0x29] & 0x88) != 0x80)
                    return 0xff;
                 return svga->crtc[svga->crtcreg];
diff --git a/src/vid_ps1_svga.c b/src/vid_ps1_svga.c
index 731bd94..8c8564f 100644
--- a/src/vid_ps1_svga.c
+++ b/src/vid_ps1_svga.c
@@ -42,9 +42,11 @@ void ps1_m2121_svga_out(uint16_t addr, uint8_t val, void *p)
         switch (addr)
         {
                 case 0x3D4:
-                svga->crtcreg = val & 0x1f;
+                svga->crtcreg = val & 0x3f;
                 return;
                 case 0x3D5:
+                if (svga->crtcreg & 0x20)
+                        return;
                 if ((svga->crtcreg < 7) && (svga->crtc[0x11] & 0x80))
                         return;
                 if ((svga->crtcreg == 7) && (svga->crtc[0x11] & 0x80))
@@ -104,7 +106,10 @@ uint8_t ps1_m2121_svga_in(uint16_t addr, void *p)
                 temp = svga->crtcreg;
                 break;
                 case 0x3D5:
-                temp = svga->crtc[svga->crtcreg];
+                if (svga->crtcreg & 0x20)
+                        temp = 0xff;
+                else
+                        temp = svga->crtc[svga->crtcreg];
                 break;
 
                 case 0x2108:
diff --git a/src/vid_vga.c b/src/vid_vga.c
index 40472f7..241166f 100644
--- a/src/vid_vga.c
+++ b/src/vid_vga.c
@@ -30,9 +30,11 @@ void vga_out(uint16_t addr, uint8_t val, void *p)
         switch (addr)
         {
                 case 0x3D4:
-                svga->crtcreg = val & 0x1f;
+                svga->crtcreg = val & 0x3f;
                 return;
                 case 0x3D5:
+                if (svga->crtcreg & 0x20)
+                        return;
                 if ((svga->crtcreg < 7) && (svga->crtc[0x11] & 0x80))
                         return;
                 if ((svga->crtcreg == 7) && (svga->crtc[0x11] & 0x80))
@@ -69,7 +71,10 @@ uint8_t vga_in(uint16_t addr, void *p)
                 temp = svga->crtcreg;
                 break;
                 case 0x3D5:
-                temp = svga->crtc[svga->crtcreg];
+                if (svga->crtcreg & 0x20)
+                        temp = 0xff;
+                else
+                        temp = svga->crtc[svga->crtcreg];
                 break;
                 default:
                 temp = svga_in(addr, svga);