diff --git a/pyiceberg/transforms.py b/pyiceberg/transforms.py
index fd90859203..32a4233c67 100644
--- a/pyiceberg/transforms.py
+++ b/pyiceberg/transforms.py
@@ -703,7 +703,7 @@ def hour_func(v: Any) -> int:
 
         elif isinstance(source, (TimestampNanoType, TimestamptzNanoType)):
 
-            def day_func(v: Any) -> int:
+            def hour_func(v: Any) -> int:
                 # python datetime has no nanoseconds support.
                 # nanosecond datetimes will be expressed as int as a workaround
                 return datetime.nanos_to_hours(v)