diff --git a/v2/sketch.py b/v2/sketch.py
index 1733942..1c5aefc 100644
--- a/v2/sketch.py
+++ b/v2/sketch.py
@@ -98,7 +98,7 @@ class Sketch:
                         default_field[k] = 'Nullable(String)'
 
                 if isinstance(v, int):
-                    default_field[k] = 'Nullable(UInt64)'
+                    default_field[k] = 'Nullable(Int64)'
 
                 if isinstance(v, float):
                     default_field[k] = 'Nullable(Float32)'