diff --git a/caravel/utils.py b/caravel/utils.py
index 9fc55c9a15f9..3c548488ac58 100644
--- a/caravel/utils.py
+++ b/caravel/utils.py
@@ -301,7 +301,7 @@ def json_iso_dttm_ser(obj):
         return val
     if isinstance(obj, datetime):
         obj = obj.isoformat()
-    if isinstance(obj, date):
+    elif isinstance(obj, date):
         obj = obj.isoformat()
     else:
         raise TypeError(