diff --git a/rasa_nlu/featurizers/regex_featurizer.py b/rasa_nlu/featurizers/regex_featurizer.py
index dbff961bce18..e594e2e6e18a 100644
--- a/rasa_nlu/featurizers/regex_featurizer.py
+++ b/rasa_nlu/featurizers/regex_featurizer.py
@@ -108,7 +108,7 @@ def persist(self, model_dir):
         if self.known_patterns:
             regex_file = os.path.join(model_dir, "regex_featurizer.json")
             with io.open(regex_file, 'w') as f:
-                f.write(str(json.dumps(self.known_patterns)))
+                f.write(str(json.dumps(self.known_patterns, indent=4)))
             return {"regex_featurizer": "regex_featurizer.json"}
         else:
             return {"regex_featurizer": None}