diff --git a/include/mgba/internal/gba/sio.h b/include/mgba/internal/gba/sio.h
index d7b702edb..07ede7009 100644
--- a/include/mgba/internal/gba/sio.h
+++ b/include/mgba/internal/gba/sio.h
@@ -54,9 +54,9 @@ struct GBASIO {
 			unsigned internalSc : 1;
 			unsigned si : 1;
 			unsigned idleSo : 1;
-			unsigned : 4;
-			unsigned start : 1;
 			unsigned : 3;
+			unsigned start : 1;
+			unsigned : 4;
 			unsigned length : 1;
 			unsigned : 1;
 			unsigned irq : 1;