diff --git a/src/core/iodev.rs b/src/core/iodev.rs
index 0e94be5..7986d89 100644
--- a/src/core/iodev.rs
+++ b/src/core/iodev.rs
@@ -121,7 +121,7 @@ impl Bus for IoDevices {
         let io_addr = addr + IO_BASE;
         match io_addr {
             REG_DISPCNT => io.gpu.dispcnt.0 = value,
-            REG_DISPSTAT => io.gpu.dispstat.0 = value & !3,
+            REG_DISPSTAT => io.gpu.dispstat.0 = value | (io.gpu.dispstat.0 & 5),
             REG_BG0CNT => io.gpu.backgrounds[0].bgcnt.0 = value,
             REG_BG1CNT => io.gpu.backgrounds[1].bgcnt.0 = value,
             REG_BG2CNT => io.gpu.backgrounds[2].bgcnt.0 = value,