diff --git a/abstract-machine/am/src/platform/nemu/ioe/gpu.c b/abstract-machine/am/src/platform/nemu/ioe/gpu.c
index cf8067e..6300ab1 100644
--- a/abstract-machine/am/src/platform/nemu/ioe/gpu.c
+++ b/abstract-machine/am/src/platform/nemu/ioe/gpu.c
@@ -34,7 +34,7 @@ void __am_gpu_fbdraw(AM_GPU_FBDRAW_T *ctl) {
       outl(FB_ADDR + w * j + i, (uint32_t)ctl->pixels + w * j + i);
     }
   }
-  if (ctl->sync) {
+  if (ctl->sync && inl(SYNC_ADDR) == 0) {
     outl(SYNC_ADDR, 1);
   }
 }