diff --git a/src/vid_voodoo.c b/src/vid_voodoo.c
index 19c5467..5d556df 100644
--- a/src/vid_voodoo.c
+++ b/src/vid_voodoo.c
@@ -414,7 +414,9 @@ static void voodoo_writel(uint32_t addr, uint32_t val, void *p)
                 
                 case SST_swapbufferCMD:
                 voodoo->cmd_written++;
+                thread_lock_mutex(voodoo->swap_mutex);
                 voodoo->swap_count++;
+                thread_unlock_mutex(voodoo->swap_mutex);
                 if (voodoo->fbiInit7 & FBIINIT7_CMDFIFO_ENABLE)
                         return;
                 voodoo_queue_command(voodoo, addr | FIFO_WRITEL_REG, val);
@@ -495,7 +497,9 @@ static void voodoo_writel(uint32_t addr, uint32_t val, void *p)
                         if ((voodoo->fbiInit1 & FBIINIT1_VIDEO_RESET) && !(val & FBIINIT1_VIDEO_RESET))
                         {
                                 voodoo->line = 0;
+                                thread_lock_mutex(voodoo->swap_mutex);
                                 voodoo->swap_count = 0;
+                                thread_unlock_mutex(voodoo->swap_mutex);
                                 voodoo->retrace_count = 0;
                         }
                         voodoo->fbiInit1 = (val & ~5) | (voodoo->fbiInit1 & 5);
@@ -1024,6 +1028,7 @@ void *voodoo_card_init()
                 voodoo->render_thread[2] = thread_create(voodoo_render_thread_3, voodoo);
                 voodoo->render_thread[3] = thread_create(voodoo_render_thread_4, voodoo);
         }
+        voodoo->swap_mutex = thread_create_mutex();
         timer_add(&voodoo->wake_timer, voodoo_wake_timer, (void *)voodoo, 0);
         
         for (c = 0; c < 0x100; c++)
@@ -1140,7 +1145,7 @@ void *voodoo_2d3d_card_init(int type)
                 voodoo->render_thread[2] = thread_create(voodoo_render_thread_3, voodoo);
                 voodoo->render_thread[3] = thread_create(voodoo_render_thread_4, voodoo);
         }
-
+        voodoo->swap_mutex = thread_create_mutex();
         timer_add(&voodoo->wake_timer, voodoo_wake_timer, (void *)voodoo, 0);
 
         for (c = 0; c < 0x100; c++)
diff --git a/src/vid_voodoo_banshee.c b/src/vid_voodoo_banshee.c
index 2026d8e..d705c57 100644
--- a/src/vid_voodoo_banshee.c
+++ b/src/vid_voodoo_banshee.c
@@ -1239,7 +1239,9 @@ static void banshee_reg_writel(uint32_t addr, uint32_t val, void *p)
                         break;
                         
                         case SST_swapPending:
+                        thread_lock_mutex(voodoo->swap_mutex);
                         voodoo->swap_count++;
+                        thread_unlock_mutex(voodoo->swap_mutex);
 //                        voodoo->cmd_written++;
                         break;
                         
@@ -1842,17 +1844,22 @@ static void banshee_vsync_callback(svga_t *svga)
         voodoo_t *voodoo = banshee->voodoo;
 
         voodoo->retrace_count++;
+        thread_lock_mutex(voodoo->swap_mutex);
         if (voodoo->swap_pending && (voodoo->retrace_count > voodoo->swap_interval))
         {
-                memset(voodoo->dirty_line, 1, 1024);
-                voodoo->retrace_count = 0;
-                banshee_set_overlay_addr(banshee, voodoo->swap_offset);
                 if (voodoo->swap_count > 0)
                         voodoo->swap_count--;
                 voodoo->swap_pending = 0;
+                thread_unlock_mutex(voodoo->swap_mutex);
+
+                memset(voodoo->dirty_line, 1, 1024);
+                voodoo->retrace_count = 0;
+                banshee_set_overlay_addr(banshee, voodoo->swap_offset);
                 thread_set_event(voodoo->wake_fifo_thread);
                 voodoo->frame_count++;
         }
+        else
+                thread_unlock_mutex(voodoo->swap_mutex);
 
         voodoo->overlay.src_y = 0;
         banshee->desktop_addr = banshee->vidDesktopStartAddr;
diff --git a/src/vid_voodoo_common.h b/src/vid_voodoo_common.h
index 637ccca..364407f 100644
--- a/src/vid_voodoo_common.h
+++ b/src/vid_voodoo_common.h
@@ -229,6 +229,7 @@ typedef struct voodoo_t
 
         uint32_t tmuConfig;
 
+        mutex_t *swap_mutex;
         int swap_count;
 
         int disp_buffer, draw_buffer;
diff --git a/src/vid_voodoo_display.c b/src/vid_voodoo_display.c
index d643d5d..a8cda43 100644
--- a/src/vid_voodoo_display.c
+++ b/src/vid_voodoo_display.c
@@ -531,6 +531,7 @@ skip_draw:
                         {
                                 voodoo_t *voodoo_1 = voodoo->set->voodoos[1];
 
+                                thread_lock_mutex(voodoo->swap_mutex);
                                 /*Only swap if both Voodoos are waiting for buffer swap*/
                                 if (voodoo->swap_pending && (voodoo->retrace_count > voodoo->swap_interval) &&
                                     voodoo_1->swap_pending && (voodoo_1->retrace_count > voodoo_1->swap_interval))
@@ -548,6 +549,7 @@ skip_draw:
                                         if (voodoo_1->swap_count > 0)
                                                 voodoo_1->swap_count--;
                                         voodoo_1->swap_pending = 0;
+                                        thread_unlock_mutex(voodoo->swap_mutex);
 
                                         thread_set_event(voodoo->wake_fifo_thread);
                                         thread_set_event(voodoo_1->wake_fifo_thread);
@@ -555,21 +557,28 @@ skip_draw:
                                         voodoo->frame_count++;
                                         voodoo_1->frame_count++;
                                 }
+                                else
+                                        thread_unlock_mutex(voodoo->swap_mutex);
                         }
                 }
                 else
                 {
+                        thread_lock_mutex(voodoo->swap_mutex);
                         if (voodoo->swap_pending && (voodoo->retrace_count > voodoo->swap_interval))
                         {
-                                memset(voodoo->dirty_line, 1, 1024);
-                                voodoo->retrace_count = 0;
                                 voodoo->front_offset = voodoo->swap_offset;
                                 if (voodoo->swap_count > 0)
                                         voodoo->swap_count--;
                                 voodoo->swap_pending = 0;
+                                thread_unlock_mutex(voodoo->swap_mutex);
+
+                                memset(voodoo->dirty_line, 1, 1024);
+                                voodoo->retrace_count = 0;
                                 thread_set_event(voodoo->wake_fifo_thread);
                                 voodoo->frame_count++;
                         }
+                        else
+                                thread_unlock_mutex(voodoo->swap_mutex);
                 }
                 voodoo->v_retrace = 1;
         }
diff --git a/src/vid_voodoo_fifo.c b/src/vid_voodoo_fifo.c
index 0d35b3a..1c807d4 100644
--- a/src/vid_voodoo_fifo.c
+++ b/src/vid_voodoo_fifo.c
@@ -90,6 +90,8 @@ void voodoo_wait_for_swap_complete(voodoo_t *voodoo)
         {
                 thread_wait_event(voodoo->wake_fifo_thread, -1);
                 thread_reset_event(voodoo->wake_fifo_thread);
+
+                thread_lock_mutex(voodoo->swap_mutex);
                 if ((voodoo->swap_pending && voodoo->flush) || FIFO_FULL)
                 {
                         /*Main thread is waiting for FIFO to empty, so skip vsync wait and just swap*/
@@ -98,8 +100,11 @@ void voodoo_wait_for_swap_complete(voodoo_t *voodoo)
                         if (voodoo->swap_count > 0)
                                 voodoo->swap_count--;
                         voodoo->swap_pending = 0;
+                        thread_unlock_mutex(voodoo->swap_mutex);
                         break;
                 }
+                else
+                        thread_unlock_mutex(voodoo->swap_mutex);
         }
 }
 
diff --git a/src/vid_voodoo_reg.c b/src/vid_voodoo_reg.c
index 965c6f6..82f4bac 100644
--- a/src/vid_voodoo_reg.c
+++ b/src/vid_voodoo_reg.c
@@ -56,8 +56,10 @@ void voodoo_reg_writel(uint32_t addr, uint32_t val, void *p)
                         if (!(val & 1))
                         {
                                 banshee_set_overlay_addr(voodoo->p, voodoo->leftOverlayBuf);
+                                thread_lock_mutex(voodoo->swap_mutex);
                                 if (voodoo->swap_count > 0)
                                         voodoo->swap_count--;
+                                thread_unlock_mutex(voodoo->swap_mutex);
                                 voodoo->frame_count++;
                         }
                         else if (TRIPLE_BUFFER)
@@ -102,8 +104,10 @@ void voodoo_reg_writel(uint32_t addr, uint32_t val, void *p)
                 {
                         memset(voodoo->dirty_line, 1, 1024);
                         voodoo->front_offset = voodoo->params.front_offset;
+                        thread_lock_mutex(voodoo->swap_mutex);
                         if (voodoo->swap_count > 0)
                                 voodoo->swap_count--;
+                        thread_unlock_mutex(voodoo->swap_mutex);
                 }
                 else if (TRIPLE_BUFFER)
                 {