diff --git a/py/bc.h b/py/bc.h
index 8709b4238..3b7b625fe 100644
--- a/py/bc.h
+++ b/py/bc.h
@@ -262,7 +262,11 @@ mp_uint_t mp_decode_uint(const byte **ptr);
 mp_uint_t mp_decode_uint_value(const byte *ptr);
 const byte *mp_decode_uint_skip(const byte *ptr);
 
-mp_vm_return_kind_t mp_execute_bytecode(mp_code_state_t *code_state, volatile mp_obj_t inject_exc);
+mp_vm_return_kind_t mp_execute_bytecode(mp_code_state_t *code_state,
+#ifndef __cplusplus
+    volatile
+#endif
+    mp_obj_t inject_exc);
 mp_code_state_t *mp_obj_fun_bc_prepare_codestate(mp_obj_t func, size_t n_args, size_t n_kw, const mp_obj_t *args);
 void mp_setup_code_state(mp_code_state_t *code_state, size_t n_args, size_t n_kw, const mp_obj_t *args);
 void mp_bytecode_print(const mp_print_t *print, const struct _mp_raw_code_t *rc, const mp_module_constants_t *cm);