diff --git a/src/crosswalk/crosswalk_builder.py b/src/crosswalk/crosswalk_builder.py
index b16b62b..3825b5a 100644
--- a/src/crosswalk/crosswalk_builder.py
+++ b/src/crosswalk/crosswalk_builder.py
@@ -151,10 +151,10 @@ class CrosswalkBuilder:
         """Create a reverse mapping where values that map to the same key are concatenated
 
         Example:
-            {"A": "1", "B": "1", "C": "2"} becomes {"1": "A, B", "2": "C"}
+            {"A": "1", "B": "1", "C": "2"} becomes {"1": ["A", "B"], "2": ["C"]}
 
         Returns:
-            dict[str, str]: Reverse mapping with concatenated values
+            dict[str, list[str]]: Reverse mapping with lists of values
         """
         reverse_dict: dict[str, list[str]] = {}
 
diff --git a/src/tests/test_crosswalk_utils.py b/src/tests/test_crosswalk_utils.py
index 19ab24c..a8722fe 100644
--- a/src/tests/test_crosswalk_utils.py
+++ b/src/tests/test_crosswalk_utils.py
@@ -140,7 +140,7 @@ def test_create_reverse_mapping():
     builder.from_dict({"A": "1", "B": "1", "C": "2", "D": "2", "E": "3"})
 
     reversed_mapping = builder.create_reverse_mapping()
-    assert reversed_mapping == {"1": "A|B", "2": "C|D", "3": "E"}
+    assert reversed_mapping == {"1": ["A", "B"], "2": ["C", "D"], "3": ["E"]}
 
 
 # Defensive programming tests