diff --git a/src/video/vid_voodoo.c b/src/video/vid_voodoo.c
index 960b913a9..6920ece5c 100644
--- a/src/video/vid_voodoo.c
+++ b/src/video/vid_voodoo.c
@@ -516,6 +516,7 @@ voodoo_writel(uint32_t addr, uint32_t val, void *priv)
                 break;
             case SST_fbiInit0:
                 if (voodoo->initEnable & 0x01) {
+                    int old_vga_pass = voodoo->fbiInit0 & FBIINIT0_VGA_PASS;
                     voodoo->fbiInit0 = val;
                     thread_wait_mutex(voodoo->force_blit_mutex);
                     voodoo->can_blit = (voodoo->fbiInit0 & FBIINIT0_VGA_PASS) ? 1 : 0;
@@ -523,6 +524,10 @@ voodoo_writel(uint32_t addr, uint32_t val, void *priv)
                         voodoo->force_blit_count = 0;
                     thread_release_mutex(voodoo->force_blit_mutex);
 
+                    /* When VGA pass-through becomes active, mark all lines dirty to force full refresh */
+                    if (!old_vga_pass && (val & FBIINIT0_VGA_PASS))
+                        memset(voodoo->dirty_line, 1, sizeof(voodoo->dirty_line));
+
                     if (voodoo->set->nr_cards == 2)
                         svga_set_override(voodoo->svga, (voodoo->set->voodoos[0]->fbiInit0 | voodoo->set->voodoos[1]->fbiInit0) & 1);
                     else
diff --git a/src/video/vid_voodoo_blitter.c b/src/video/vid_voodoo_blitter.c
index d4b316dc5..87127a949 100644
--- a/src/video/vid_voodoo_blitter.c
+++ b/src/video/vid_voodoo_blitter.c
@@ -506,6 +506,9 @@ voodoo_fastfill(voodoo_t *voodoo, voodoo_params_t *params)
                     for (int x = params->clipLeft; x < params->clipRight; x++)
                         cbuf[x] = col;
                 }
+                /* Mark line dirty for single buffer mode */
+                if (params->draw_offset == params->front_offset && y < 2048)
+                    voodoo->dirty_line[y] = 1;
             }
         }
     }
diff --git a/src/video/vid_voodoo_render.c b/src/video/vid_voodoo_render.c
index 19dedfa7a..1c0edf775 100644
--- a/src/video/vid_voodoo_render.c
+++ b/src/video/vid_voodoo_render.c
@@ -1389,10 +1389,9 @@ skip_pixel:
         voodoo->texel_count[odd_even] += state->texel_count;
         voodoo->fbiPixelsIn += state->pixel_count;
 
-        if (voodoo->params.draw_offset == voodoo->params.front_offset) {
-            int dirty_idx = SLI_ENABLED ? (real_y >> 1) : real_y;
-            if (dirty_idx < 2048)
-                voodoo->dirty_line[dirty_idx] = 1;
+        if (voodoo->params.draw_offset == voodoo->params.front_offset && !SLI_ENABLED) {
+            if (real_y < 2048)
+                voodoo->dirty_line[real_y] = 1;
         }
 
 next_line: