diff --git a/yt/data_objects/selection_objects/region.py b/yt/data_objects/selection_objects/region.py
index 9e100e19a0..bdee983b03 100644
--- a/yt/data_objects/selection_objects/region.py
+++ b/yt/data_objects/selection_objects/region.py
@@ -57,12 +57,16 @@ def __init__(
             self.left_edge = self.ds.arr(left_edge, "code_length", dtype="float64")
         else:
             # need to assign this dataset's unit registry to the YTArray
-            self.left_edge = self.ds.arr(left_edge.copy(), dtype="float64")
+            # and convert to code_length to ensure consistent units for selection
+            left_edge_arr = self.ds.arr(left_edge.copy(), dtype="float64")
+            self.left_edge = left_edge_arr.to("code_length")
         if not isinstance(right_edge, YTArray):
             self.right_edge = self.ds.arr(right_edge, "code_length", dtype="float64")
         else:
             # need to assign this dataset's unit registry to the YTArray
-            self.right_edge = self.ds.arr(right_edge.copy(), dtype="float64")
+            # and convert to code_length to ensure consistent units for selection
+            right_edge_arr = self.ds.arr(right_edge.copy(), dtype="float64")
+            self.right_edge = right_edge_arr.to("code_length")
 
     def _get_bbox(self):
         """