diff --git a/mace/python/tools/str2vec_maps.cc.jinja2 b/mace/python/tools/str2vec_maps.cc.jinja2
index 332fe0269742ff667de95a5e5f4a81b634072f70..a9e92865a375260a1fb97765d5f1127ac1604951 100644
--- a/mace/python/tools/str2vec_maps.cc.jinja2
+++ b/mace/python/tools/str2vec_maps.cc.jinja2
@@ -22,7 +22,7 @@ namespace mace {
 
 extern const std::map<std::string, std::vector<{{data_type}}>> {{variable_name}} =
 {
-  {% for key, value in maps.iteritems() %}
+  {% for key, value in maps.items() %}
   {
     "{{key}}",
     {