diff --git a/cmac.h b/cmac.h
index 9d972ea5a9b0098bda92a3527573c9d1358a16ce..9bff537d7748ea11497f8ea8628d71d305d946e0 100644
--- a/cmac.h
+++ b/cmac.h
@@ -69,8 +69,8 @@ struct cmac128_ctx
   union nettle_block16 X;
 
   /* Block buffer */
-  size_t index;
   union nettle_block16 block;
+  size_t index;
 };
 
 void