diff --git a/CHANGES.rst b/CHANGES.rst
index 660ecb2c..b4ff2f05 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -3,6 +3,14 @@
 Changelog
 =========
 
+2.2.1 (unreleased)
+------------------
+Contributors to this version: Ludwig Lierhammer (:user:`ludwiglierhammer`)
+
+Bug fixes
+^^^^^^^^^
+* ``cdm_reader_mapper.cdm_mapper``: set indexes to input data indexed when setting default values (:pull:`356`)
+
 2.2.0 (2026-01-23)
 ------------------
 Contributors to this version: Ludwig Lierhammer (:user:`ludwiglierhammer`) and Joseph Siddons (:user:`jtsiddons`)
diff --git a/cdm_reader_mapper/cdm_mapper/mapper.py b/cdm_reader_mapper/cdm_mapper/mapper.py
index 7013a725..1cd61314 100755
--- a/cdm_reader_mapper/cdm_mapper/mapper.py
+++ b/cdm_reader_mapper/cdm_mapper/mapper.py
@@ -213,7 +213,7 @@ def _extract_input_data(idata, elements, cols, default, logger):
     """Extract the relevant input data based on `elements`."""
 
     def _return_default():
-        return pd.Series(_default(default, len(idata))), True
+        return pd.Series(_default(default, len(idata)), index=idata.index), True
 
     if not elements:
         return _return_default()