diff --git a/py/objexcept.c b/py/objexcept.c
index d5c056a8d9..dbe702fa9e 100644
--- a/py/objexcept.c
+++ b/py/objexcept.c
@@ -66,30 +66,34 @@ const mp_obj_type_t mp_type_BaseException = {
     .make_new = mp_obj_exception_make_new,
 };
 
-#define MP_DEFINE_EXCEPTION(exc_name) \
-STATIC const mp_obj_tuple_t mp_type_ ## exc_name ## _bases_tuple = {{&tuple_type}, 1, {(mp_obj_t)&mp_type_BaseException}};\
+#define MP_DEFINE_EXCEPTION_BASE(base_name) \
+STATIC const mp_obj_tuple_t mp_type_ ## base_name ## _base_tuple = {{&tuple_type}, 1, {(mp_obj_t)&mp_type_ ## base_name}};\
+
+#define MP_DEFINE_EXCEPTION(exc_name, base_name) \
 const mp_obj_type_t mp_type_ ## exc_name = { \
     { &mp_type_type }, \
     .name = MP_QSTR_ ## exc_name, \
     .print = mp_obj_exception_print, \
     .make_new = mp_obj_exception_make_new, \
-    .bases_tuple = (mp_obj_t)&mp_type_ ## exc_name ## _bases_tuple, \
+    .bases_tuple = (mp_obj_t)&mp_type_ ## base_name ## _base_tuple, \
 };
 
-MP_DEFINE_EXCEPTION(AssertionError)
-MP_DEFINE_EXCEPTION(AttributeError)
-MP_DEFINE_EXCEPTION(ImportError)
-MP_DEFINE_EXCEPTION(IndentationError)
-MP_DEFINE_EXCEPTION(IndexError)
-MP_DEFINE_EXCEPTION(KeyError)
-MP_DEFINE_EXCEPTION(NameError)
-MP_DEFINE_EXCEPTION(SyntaxError)
-MP_DEFINE_EXCEPTION(TypeError)
-MP_DEFINE_EXCEPTION(ValueError)
-MP_DEFINE_EXCEPTION(OverflowError)
-MP_DEFINE_EXCEPTION(OSError)
-MP_DEFINE_EXCEPTION(NotImplementedError)
-MP_DEFINE_EXCEPTION(StopIteration)
+MP_DEFINE_EXCEPTION_BASE(BaseException)
+
+MP_DEFINE_EXCEPTION(AssertionError, BaseException)
+MP_DEFINE_EXCEPTION(AttributeError, BaseException)
+MP_DEFINE_EXCEPTION(ImportError, BaseException)
+MP_DEFINE_EXCEPTION(IndentationError, BaseException)
+MP_DEFINE_EXCEPTION(IndexError, BaseException)
+MP_DEFINE_EXCEPTION(KeyError, BaseException)
+MP_DEFINE_EXCEPTION(NameError, BaseException)
+MP_DEFINE_EXCEPTION(SyntaxError, BaseException)
+MP_DEFINE_EXCEPTION(TypeError, BaseException)
+MP_DEFINE_EXCEPTION(ValueError, BaseException)
+MP_DEFINE_EXCEPTION(OverflowError, BaseException)
+MP_DEFINE_EXCEPTION(OSError, BaseException)
+MP_DEFINE_EXCEPTION(NotImplementedError, BaseException)
+MP_DEFINE_EXCEPTION(StopIteration, BaseException)
 
 mp_obj_t mp_obj_new_exception(const mp_obj_type_t *exc_type) {
     return mp_obj_new_exception_msg_varg(exc_type, NULL);
diff --git a/py/runtime.c b/py/runtime.c
index aa7940fd8e..798f7b671c 100644
--- a/py/runtime.c
+++ b/py/runtime.c
@@ -1003,6 +1003,8 @@ mp_obj_t rt_make_raise_obj(mp_obj_t o) {
     if (mp_obj_is_exception_type(o)) {
         // o is an exception type (it is derived from BaseException (or is BaseException))
         // create and return a new exception instance by calling o
+        // TODO could have an option to disable traceback, then builtin exceptions (eg TypeError)
+        // could have const instances in ROM which we return here instead
         return rt_call_function_n_kw(o, 0, 0, NULL);
     } else if (mp_obj_is_exception_instance(o)) {
         // o is an instance of an exception, so use it as the exception