diff --git a/am/src/nemu/include/nemu.h b/am/src/nemu/include/nemu.h
index 889d536..d629db3 100644
--- a/am/src/nemu/include/nemu.h
+++ b/am/src/nemu/include/nemu.h
@@ -19,13 +19,13 @@
 # define SERIAL_PORT  0x3f8
 # define KBD_ADDR     0x60
 # define RTC_ADDR     0x48
-# define SCREEN_ADDR  0x100
+# define VGACTL_ADDR  0x100
 # define AUDIO_ADDR   0x200
 #else
 # define SERIAL_PORT  0xa10003f8
 # define KBD_ADDR     0xa1000060
 # define RTC_ADDR     0xa1000048
-# define SCREEN_ADDR  0xa1000100
+# define VGACTL_ADDR  0xa1000100
 # define AUDIO_ADDR   0xa1000200
 #endif
 
diff --git a/am/src/nemu/ioe/gpu.c b/am/src/nemu/ioe/gpu.c
index b20c743..fb33096 100644
--- a/am/src/nemu/ioe/gpu.c
+++ b/am/src/nemu/ioe/gpu.c
@@ -1,7 +1,7 @@
 #include <am.h>
 #include <nemu.h>
 
-#define SYNC_ADDR (SCREEN_ADDR + 4)
+#define SYNC_ADDR (VGACTL_ADDR + 4)
 
 void __am_gpu_init() {
 }
@@ -16,7 +16,7 @@ void __am_gpu_config(AM_GPU_CONFIG_T *cfg) {
 
 void __am_gpu_fbdraw(AM_GPU_FBDRAW_T *ctl) {
   if (ctl->sync) {
-    outl(SYNC_ADDR, 0);
+    outl(SYNC_ADDR, 1);
   }
 }