diff --git a/modin/engines/base/frame/data.py b/modin/engines/base/frame/data.py
index 0f863c063f2..de8aef66674 100644
--- a/modin/engines/base/frame/data.py
+++ b/modin/engines/base/frame/data.py
@@ -1729,7 +1729,10 @@ def _copartition(
             )
 
         index_other_obj = [o.axes[axis] for o in other]
-        joined_index = self._join_index_objects(axis, index_other_obj, how, sort)
+        if how == "reindex_to_self":
+            joined_index = self.axes[axis]
+        else:
+            joined_index = self._join_index_objects(axis, index_other_obj, how, sort)
 
         # We have to set these because otherwise when we perform the functions it may
         # end up serializing this entire object.
diff --git a/modin/pandas/dataframe.py b/modin/pandas/dataframe.py
index 9ffbb82ef55..8bb6609552f 100644
--- a/modin/pandas/dataframe.py
+++ b/modin/pandas/dataframe.py
@@ -1975,7 +1975,7 @@ def __setitem__(self, key, value):
                         self._query_compiler.concat(
                             1,
                             value._query_compiler,
-                            join="left",
+                            join="reindex_to_self",
                         ),
                         inplace=True,
                     )