diff --git a/py/emitglue.c b/py/emitglue.c
index 0e13fd6d1f..996b79e173 100644
--- a/py/emitglue.c
+++ b/py/emitglue.c
@@ -67,12 +67,12 @@ void mp_emit_glue_assign_bytecode(mp_raw_code_t *rc, const byte *code,
 
     rc->kind = MP_CODE_BYTECODE;
     rc->scope_flags = scope_flags;
-    rc->data.u_byte.bytecode = code;
-    rc->data.u_byte.const_table = const_table;
+    rc->fun_data = code;
+    rc->const_table = const_table;
     #if MICROPY_PERSISTENT_CODE_SAVE
-    rc->data.u_byte.bc_len = len;
-    rc->data.u_byte.n_obj = n_obj;
-    rc->data.u_byte.n_raw_code = n_raw_code;
+    rc->fun_data_len = len;
+    rc->n_obj = n_obj;
+    rc->n_raw_code = n_raw_code;
     #endif
 
 #ifdef DEBUG_PRINT
@@ -94,9 +94,9 @@ void mp_emit_glue_assign_native(mp_raw_code_t *rc, mp_raw_code_kind_t kind, void
     rc->kind = kind;
     rc->scope_flags = scope_flags;
     rc->n_pos_args = n_pos_args;
-    rc->data.u_native.fun_data = fun_data;
-    rc->data.u_native.const_table = const_table;
-    rc->data.u_native.type_sig = type_sig;
+    rc->fun_data = fun_data;
+    rc->const_table = const_table;
+    rc->type_sig = type_sig;
 
 #ifdef DEBUG_PRINT
     DEBUG_printf("assign native: kind=%d fun=%p len=" UINT_FMT " n_pos_args=" UINT_FMT " flags=%x\n", kind, fun_data, fun_len, n_pos_args, (uint)scope_flags);
@@ -135,7 +135,7 @@ mp_obj_t mp_make_function_from_raw_code(const mp_raw_code_t *rc, mp_obj_t def_ar
         #if MICROPY_EMIT_NATIVE
         case MP_CODE_NATIVE_PY:
         case MP_CODE_NATIVE_VIPER:
-            fun = mp_obj_new_fun_native(def_args, def_kw_args, rc->data.u_native.fun_data, rc->data.u_native.const_table);
+            fun = mp_obj_new_fun_native(def_args, def_kw_args, rc->fun_data, rc->const_table);
             // Check for a generator function, and if so change the type of the object
             if ((rc->scope_flags & MP_SCOPE_FLAG_GENERATOR) != 0) {
                 ((mp_obj_base_t*)MP_OBJ_TO_PTR(fun))->type = &mp_type_native_gen_wrap;
@@ -144,13 +144,13 @@ mp_obj_t mp_make_function_from_raw_code(const mp_raw_code_t *rc, mp_obj_t def_ar
         #endif
         #if MICROPY_EMIT_INLINE_ASM
         case MP_CODE_NATIVE_ASM:
-            fun = mp_obj_new_fun_asm(rc->n_pos_args, rc->data.u_native.fun_data, rc->data.u_native.type_sig);
+            fun = mp_obj_new_fun_asm(rc->n_pos_args, rc->fun_data, rc->type_sig);
             break;
         #endif
         default:
             // rc->kind should always be set and BYTECODE is the only remaining case
             assert(rc->kind == MP_CODE_BYTECODE);
-            fun = mp_obj_new_fun_bc(def_args, def_kw_args, rc->data.u_byte.bytecode, rc->data.u_byte.const_table);
+            fun = mp_obj_new_fun_bc(def_args, def_kw_args, rc->fun_data, rc->const_table);
             // check for generator functions and if so change the type of the object
             if ((rc->scope_flags & MP_SCOPE_FLAG_GENERATOR) != 0) {
                 ((mp_obj_base_t*)MP_OBJ_TO_PTR(fun))->type = &mp_type_gen_wrap;
diff --git a/py/emitglue.h b/py/emitglue.h
index d39a10ee94..53049b161e 100644
--- a/py/emitglue.h
+++ b/py/emitglue.h
@@ -52,22 +52,16 @@ typedef struct _mp_raw_code_t {
     mp_uint_t kind : 3; // of type mp_raw_code_kind_t
     mp_uint_t scope_flags : 7;
     mp_uint_t n_pos_args : 11;
-    union {
-        struct {
-            const byte *bytecode;
-            const mp_uint_t *const_table;
-            #if MICROPY_PERSISTENT_CODE_SAVE
-            mp_uint_t bc_len;
-            uint16_t n_obj;
-            uint16_t n_raw_code;
-            #endif
-        } u_byte;
-        struct {
-            void *fun_data;
-            const mp_uint_t *const_table;
-            mp_uint_t type_sig; // for viper, compressed as 2-bit types; ret is MSB, then arg0, arg1, etc
-        } u_native;
-    } data;
+    const void *fun_data;
+    const mp_uint_t *const_table;
+    #if MICROPY_PERSISTENT_CODE_SAVE
+    size_t fun_data_len;
+    uint16_t n_obj;
+    uint16_t n_raw_code;
+    #endif
+    #if MICROPY_EMIT_NATIVE || MICROPY_EMIT_INLINE_ASM
+    mp_uint_t type_sig; // for viper, compressed as 2-bit types; ret is MSB, then arg0, arg1, etc
+    #endif
 } mp_raw_code_t;
 
 mp_raw_code_t *mp_emit_glue_new_raw_code(void);
diff --git a/py/persistentcode.c b/py/persistentcode.c
index c0a3281113..d4ca50e81f 100644
--- a/py/persistentcode.c
+++ b/py/persistentcode.c
@@ -449,16 +449,16 @@ STATIC void save_raw_code(mp_print_t *print, mp_raw_code_t *rc, qstr_window_t *q
     }
 
     // extract prelude
-    const byte *ip = rc->data.u_byte.bytecode;
+    const byte *ip = rc->fun_data;
     const byte *ip2;
     bytecode_prelude_t prelude;
     extract_prelude(&ip, &ip2, &prelude);
 
     // save prelude
-    size_t prelude_len = ip - rc->data.u_byte.bytecode;
-    const byte *ip_top = rc->data.u_byte.bytecode + rc->data.u_byte.bc_len;
-    mp_print_uint(print, rc->data.u_byte.bc_len);
-    mp_print_bytes(print, rc->data.u_byte.bytecode, prelude_len);
+    size_t prelude_len = ip - rc->fun_data;
+    const byte *ip_top = rc->fun_data + rc->fun_data_len;
+    mp_print_uint(print, rc->fun_data_len);
+    mp_print_bytes(print, rc->fun_data, prelude_len);
 
     // save bytecode
     save_bytecode(print, qstr_window, ip, ip_top);
@@ -468,17 +468,17 @@ STATIC void save_raw_code(mp_print_t *print, mp_raw_code_t *rc, qstr_window_t *q
     save_qstr(print, qstr_window, ip2[2] | (ip2[3] << 8)); // source_file
 
     // save constant table
-    mp_print_uint(print, rc->data.u_byte.n_obj);
-    mp_print_uint(print, rc->data.u_byte.n_raw_code);
-    const mp_uint_t *const_table = rc->data.u_byte.const_table;
+    mp_print_uint(print, rc->n_obj);
+    mp_print_uint(print, rc->n_raw_code);
+    const mp_uint_t *const_table = rc->const_table;
     for (uint i = 0; i < prelude.n_pos_args + prelude.n_kwonly_args; ++i) {
         mp_obj_t o = (mp_obj_t)*const_table++;
         save_qstr(print, qstr_window, MP_OBJ_QSTR_VALUE(o));
     }
-    for (uint i = 0; i < rc->data.u_byte.n_obj; ++i) {
+    for (uint i = 0; i < rc->n_obj; ++i) {
         save_obj(print, (mp_obj_t)*const_table++);
     }
-    for (uint i = 0; i < rc->data.u_byte.n_raw_code; ++i) {
+    for (uint i = 0; i < rc->n_raw_code; ++i) {
         save_raw_code(print, (mp_raw_code_t*)(uintptr_t)*const_table++, qstr_window);
     }
 }
diff --git a/tools/mpy-tool.py b/tools/mpy-tool.py
index 8a82374031..37adaf3556 100755
--- a/tools/mpy-tool.py
+++ b/tools/mpy-tool.py
@@ -391,18 +391,16 @@ class RawCode:
         print('    .kind = MP_CODE_BYTECODE,')
         print('    .scope_flags = 0x%02x,' % self.prelude[2])
         print('    .n_pos_args = %u,' % self.prelude[3])
-        print('    .data.u_byte = {')
-        print('        .bytecode = bytecode_data_%s,' % self.escaped_name)
+        print('    .fun_data = bytecode_data_%s,' % self.escaped_name)
         if const_table_len:
-            print('        .const_table = (mp_uint_t*)const_table_data_%s,' % self.escaped_name)
+            print('    .const_table = (mp_uint_t*)const_table_data_%s,' % self.escaped_name)
         else:
-            print('        .const_table = NULL,')
-        print('        #if MICROPY_PERSISTENT_CODE_SAVE')
-        print('        .bc_len = %u,' % len(self.bytecode))
-        print('        .n_obj = %u,' % len(self.objs))
-        print('        .n_raw_code = %u,' % len(self.raw_codes))
-        print('        #endif')
-        print('    },')
+            print('    .const_table = NULL,')
+        print('    #if MICROPY_PERSISTENT_CODE_SAVE')
+        print('    .fun_data_len = %u,' % len(self.bytecode))
+        print('    .n_obj = %u,' % len(self.objs))
+        print('    .n_raw_code = %u,' % len(self.raw_codes))
+        print('    #endif')
         print('};')
 
 class BytecodeBuffer: