diff --git a/py/obj.h b/py/obj.h
index 80294b3b4f..d28623e64c 100644
--- a/py/obj.h
+++ b/py/obj.h
@@ -629,7 +629,7 @@ mp_obj_t mp_obj_new_fun_native(mp_obj_t def_args_in, mp_obj_t def_kw_args, const
 mp_obj_t mp_obj_new_fun_viper(size_t n_args, void *fun_data, mp_uint_t type_sig);
 mp_obj_t mp_obj_new_fun_asm(size_t n_args, void *fun_data, mp_uint_t type_sig);
 mp_obj_t mp_obj_new_gen_wrap(mp_obj_t fun);
-mp_obj_t mp_obj_new_closure(mp_obj_t fun, mp_uint_t n_closed, const mp_obj_t *closed);
+mp_obj_t mp_obj_new_closure(mp_obj_t fun, size_t n_closed, const mp_obj_t *closed);
 mp_obj_t mp_obj_new_tuple(size_t n, const mp_obj_t *items);
 mp_obj_t mp_obj_new_list(size_t n, mp_obj_t *items);
 mp_obj_t mp_obj_new_dict(size_t n_args);
diff --git a/py/objclosure.c b/py/objclosure.c
index 4b37d2dd12..3e12358bbd 100644
--- a/py/objclosure.c
+++ b/py/objclosure.c
@@ -32,7 +32,7 @@
 typedef struct _mp_obj_closure_t {
     mp_obj_base_t base;
     mp_obj_t fun;
-    mp_uint_t n_closed;
+    size_t n_closed;
     mp_obj_t closed[];
 } mp_obj_closure_t;
 
@@ -41,7 +41,7 @@ STATIC mp_obj_t closure_call(mp_obj_t self_in, size_t n_args, size_t n_kw, const
 
     // need to concatenate closed-over-vars and args
 
-    mp_uint_t n_total = self->n_closed + n_args + 2 * n_kw;
+    size_t n_total = self->n_closed + n_args + 2 * n_kw;
     if (n_total <= 5) {
         // use stack to allocate temporary args array
         mp_obj_t args2[5];
@@ -66,7 +66,7 @@ STATIC void closure_print(const mp_print_t *print, mp_obj_t o_in, mp_print_kind_
     mp_print_str(print, "<closure ");
     mp_obj_print_helper(print, o->fun, PRINT_REPR);
     mp_printf(print, " at %p, n_closed=%u ", o, (int)o->n_closed);
-    for (mp_uint_t i = 0; i < o->n_closed; i++) {
+    for (size_t i = 0; i < o->n_closed; i++) {
         if (o->closed[i] == MP_OBJ_NULL) {
             mp_print_str(print, "(nil)");
         } else {
@@ -87,7 +87,7 @@ const mp_obj_type_t closure_type = {
     .call = closure_call,
 };
 
-mp_obj_t mp_obj_new_closure(mp_obj_t fun, mp_uint_t n_closed_over, const mp_obj_t *closed) {
+mp_obj_t mp_obj_new_closure(mp_obj_t fun, size_t n_closed_over, const mp_obj_t *closed) {
     mp_obj_closure_t *o = m_new_obj_var(mp_obj_closure_t, mp_obj_t, n_closed_over);
     o->base.type = &closure_type;
     o->fun = fun;