diff --git a/micropython/firmware/mpconfigport.h b/micropython/firmware/mpconfigport.h
index d64f5706..c780b227 100644
--- a/micropython/firmware/mpconfigport.h
+++ b/micropython/firmware/mpconfigport.h
@@ -146,6 +146,8 @@ extern const struct _mp_obj_module_t mp_module_TrezorUtils;
 
 // type definitions for the specific machine
 
+#define BYTES_PER_WORD (4)
+
 #define MICROPY_MAKE_POINTER_CALLABLE(p) ((void*)((mp_uint_t)(p) | 1))
 
 #define MP_SSIZE_MAX (0x0fffffff)