diff --git a/Smartscope/core/selectors.py b/Smartscope/core/selectors.py
index 14062c92..0fdafb47 100755
--- a/Smartscope/core/selectors.py
+++ b/Smartscope/core/selectors.py
@@ -14,7 +14,7 @@
 logger = logging.getLogger(__name__)
 
 
-def generate_equal_clusters(parent, targets, n_groups, extra_fields):
+def generate_equal_clusters(parent, targets, n_groups, extra_fields=dict()):
     output = list()
     if len(targets) > 0:
         split_targets = np.array_split(targets, n_groups)