diff --git a/py/objmap.c b/py/objmap.c
index 0b2189016e..111c964fdd 100644
--- a/py/objmap.c
+++ b/py/objmap.c
@@ -31,7 +31,7 @@
 
 typedef struct _mp_obj_map_t {
     mp_obj_base_t base;
-    mp_uint_t n_iters;
+    size_t n_iters;
     mp_obj_t fun;
     mp_obj_t iters[];
 } mp_obj_map_t;
@@ -42,7 +42,7 @@ STATIC mp_obj_t map_make_new(const mp_obj_type_t *type, size_t n_args, size_t n_
     o->base.type = type;
     o->n_iters = n_args - 1;
     o->fun = args[0];
-    for (mp_uint_t i = 0; i < n_args - 1; i++) {
+    for (size_t i = 0; i < n_args - 1; i++) {
         o->iters[i] = mp_getiter(args[i + 1], NULL);
     }
     return MP_OBJ_FROM_PTR(o);
@@ -53,7 +53,7 @@ STATIC mp_obj_t map_iternext(mp_obj_t self_in) {
     mp_obj_map_t *self = MP_OBJ_TO_PTR(self_in);
     mp_obj_t *nextses = m_new(mp_obj_t, self->n_iters);
 
-    for (mp_uint_t i = 0; i < self->n_iters; i++) {
+    for (size_t i = 0; i < self->n_iters; i++) {
         mp_obj_t next = mp_iternext(self->iters[i]);
         if (next == MP_OBJ_STOP_ITERATION) {
             m_del(mp_obj_t, nextses, self->n_iters);