diff --git a/src/minimization/config/optimize_kl_config.py b/src/minimization/config/optimize_kl_config.py
index e5a0402564d64a979b2a549fe3313fe05934ea6a..d5f1f5b4a3be0f78401be0dec1a14e947e285d00 100644
--- a/src/minimization/config/optimize_kl_config.py
+++ b/src/minimization/config/optimize_kl_config.py
@@ -81,7 +81,7 @@ class OptimizeKLConfig:
     `optionxform` to `str` before parsing.
     """
 
-    def __init__(self, config_parser, builders):
+    def __init__(self, config_parser, builders={}):
         if not isinstance(config_parser, ConfigParser):
             raise TypeError
         if config_parser.optionxform != str: