diff --git a/src/vid_tgui9440.c b/src/vid_tgui9440.c
index 0014cc5..de748b0 100644
--- a/src/vid_tgui9440.c
+++ b/src/vid_tgui9440.c
@@ -311,6 +311,7 @@ void tgui_out(uint16_t addr, uint8_t val, void *p)
                                 {
                                         tgui->linear_base = ((val & 0xf) | ((val >> 2) & 0x30)) << 20;
                                         tgui->linear_size = (val & 0x10) ? 0x200000 : 0x100000;
+                                        tgui->svga.decode_mask = (val & 0x10) ? 0x1fffff : 0xfffff;
                                 }
         			tgui_recalcmapping(tgui);
                         }
@@ -710,12 +711,14 @@ void tgui_pci_write(int func, int addr, uint8_t val, void *p)
                 case 0x12:
                 tgui->linear_base = (tgui->linear_base & 0xff000000) | ((val & 0xe0) << 16);
                 tgui->linear_size = 2 << 20;
+                tgui->svga.decode_mask = 0x1fffff;
                 svga->crtc[0x21] = (svga->crtc[0x21] & ~0xf) | (val >> 4);
                 tgui_recalcmapping(tgui);
                 break;
                 case 0x13:
                 tgui->linear_base = (tgui->linear_base & 0xe00000) | (val << 24);
                 tgui->linear_size = 2 << 20;
+                tgui->svga.decode_mask = 0x1fffff;
                 svga->crtc[0x21] = (svga->crtc[0x21] & ~0xc0) | (val >> 6);
                 tgui_recalcmapping(tgui);
                 break;