diff --git a/py/map.c b/py/map.c
index 9f919e06ae..2bae8b28d7 100644
--- a/py/map.c
+++ b/py/map.c
@@ -40,6 +40,17 @@ mp_map_t *mp_map_new(int n) {
     return map;
 }
 
+// Differentiate from mp_map_clear() - semantics is different
+void mp_map_deinit(mp_map_t *map) {
+    m_del(mp_map_elem_t, map->table, map->alloc);
+    map->used = map->alloc = 0;
+}
+
+void mp_map_free(mp_map_t *map) {
+    mp_map_deinit(map);
+    m_del_obj(mp_map_t, map);
+}
+
 void mp_map_clear(mp_map_t *map) {
     map->used = 0;
     map->all_keys_are_qstrs = 1;
diff --git a/py/map.h b/py/map.h
index 2db0ac3ebc..7acb5a98a7 100644
--- a/py/map.h
+++ b/py/map.h
@@ -28,6 +28,8 @@ typedef enum _mp_map_lookup_kind_t {
 int get_doubling_prime_greater_or_equal_to(int x);
 void mp_map_init(mp_map_t *map, int n);
 mp_map_t *mp_map_new(int n);
+void mp_map_deinit(mp_map_t *map);
+void mp_map_free(mp_map_t *map);
 mp_map_elem_t* mp_map_lookup(mp_map_t *map, mp_obj_t index, mp_map_lookup_kind_t lookup_kind);
 void mp_map_clear(mp_map_t *map);
 
diff --git a/py/runtime.c b/py/runtime.c
index 976d23a6b9..8ad98d5f12 100644
--- a/py/runtime.c
+++ b/py/runtime.c
@@ -166,6 +166,7 @@ void rt_init(void) {
 
     mp_module_micropython_init();
 
+    // TODO: wastes one mp_code_t structure in mem
     next_unique_code_id = 1; // 0 indicates "no code"
     unique_codes_alloc = 0;
     unique_codes = NULL;
@@ -177,6 +178,9 @@ void rt_init(void) {
 
 void rt_deinit(void) {
     m_del(mp_code_t, unique_codes, unique_codes_alloc);
+    mp_map_free(map_globals);
+    mp_map_deinit(&map_loaded_modules);
+    mp_map_deinit(&map_builtins);
 #ifdef WRITE_CODE
     if (fp_write_code != NULL) {
         fclose(fp_write_code);