diff --git a/nemu/src/device/vga.c b/nemu/src/device/vga.c
index 4914906..0e4118c 100644
--- a/nemu/src/device/vga.c
+++ b/nemu/src/device/vga.c
@@ -75,7 +75,7 @@ static inline void update_screen() {
 void vga_update_screen() {
   // TODO: call `update_screen()` when the sync register is non-zero,
   // then zero out the sync register
-  if (*sync_reg) {
+  if (*sync_reg != 0) {
     update_screen();
     *sync_reg = 0;
   }