diff --git a/app/__init__.py b/app/__init__.py
index e9953eec..428ba164 100644
--- a/app/__init__.py
+++ b/app/__init__.py
@@ -119,7 +119,7 @@ def handle_invalid_usage(error):
 # JSON ENCODING
 class ScoDocJSONEncoder(JSONEncoder):
     def default(self, o):
-        if isinstance(o, datetime.datetime):
+        if isinstance(o, (datetime.datetime, datetime.date)):
             return o.isoformat()
 
         return super().default(o)