diff --git a/u2/list_ops.py b/u2/list_ops.py
index 43fcd5f..068983e 100644
--- a/u2/list_ops.py
+++ b/u2/list_ops.py
@@ -1,5 +1,4 @@
 
-
 def append(list1, list2):
     result = []
     for item in list1:
@@ -10,7 +9,7 @@ def append(list1, list2):
 
 def concat(lists):
     result = []
-    for sublist in lists
+    for sublist in lists:
         result = append(result, sublist)
     return result