diff --git a/README.md b/README.md
index 4841e3c..d3c65df 100644
--- a/README.md
+++ b/README.md
@@ -174,7 +174,7 @@ schema = ...
 ```
 - `tsm_concat` - Trim string with max lenght. Use `$self` to point on field value. Example:
 ```
-data = {"id": "dataset-1}
+data = {"id": "dataset-1"}
 
 schema = ...
     "package_url": {
@@ -198,7 +198,25 @@ There is a possibility to provide more arguments to a validator like in `tsm_get
 
 - `tsm_mapper` - Map current value to the mapping dict
 
-Map a value to another value. The current value must serve as a key within the mapping dictionary, while the new value will represent the updated value
+Map a value to another value. The current value must serve as a key within the mapping dictionary, while the new value will represent the updated value.
+
+The default value to be used when the key is not found in the mapping. If the default value is not provided, the current value will be used as it.
+
+```
+data = {"language": "English"}
+
+schema = ...
+    "language": {
+        "validators": [
+            [
+                "tsm_mapper",
+                {"English": "eng"},
+                "English",
+            ]
+        ],
+    },
+    ...
+```
 
 ### Keywords
 1. `map_to` (`str`) - changes the `field.name` in result dict.
diff --git a/ckanext/transmute/tests/test_transmutators.py b/ckanext/transmute/tests/test_transmutators.py
index e298a17..00994e3 100644
--- a/ckanext/transmute/tests/test_transmutators.py
+++ b/ckanext/transmute/tests/test_transmutators.py
@@ -368,6 +368,9 @@ def test_default_allows_falsy_values(self, default):
 
         assert result == {"field_name": default}
 
+
+@pytest.mark.ckan_config("ckan.plugins", "scheming_datasets")
+class TestMapperTransmutator:
     def test_mapper_with_mapped_value(self):
         data: dict[str, Any] = {"language": "eng"}
 
@@ -390,7 +393,6 @@ def test_mapper_with_mapped_value(self):
 
         assert result["language"] == "English"
 
-
     def test_mapper_without_mapped_value(self):
         data: dict[str, Any] = {"language": "ua"}
 
@@ -413,14 +415,14 @@ def test_mapper_without_mapped_value(self):
 
         assert result["language"] == "Spanish"
 
-    def test_mapper_without_default(self):
+    def test_mapper_without_mapping(self):
         data: dict[str, Any] = {"language": "ua"}
 
         tsm_schema = build_schema(
             {
                 "language": {
                     "validators": [
-                        ["tsm_mapper", {"eng": "English"}],
+                        ["tsm_mapper"],
                     ],
                 },
             }
@@ -434,4 +436,26 @@ def test_mapper_without_default(self):
                 root="Dataset",
             )
 
-        assert e.value.error == "mapper() missing 1 required positional argument: 'default'"
+        assert e.value.error == "Arguments for validator weren't provided"
+
+    def test_mapper_without_default(self):
+        data: dict[str, Any] = {"language": "ua"}
+
+        tsm_schema = build_schema(
+            {
+                "language": {
+                    "validators": [
+                        ["tsm_mapper", {"eng": "English"}],
+                    ],
+                },
+            }
+        )
+
+        result = call_action(
+            "tsm_transmute",
+            data=data,
+            schema=tsm_schema,
+            root="Dataset",
+        )
+
+        assert result["language"] == "ua"
diff --git a/ckanext/transmute/transmutators.py b/ckanext/transmute/transmutators.py
index fbe7555..d517d5e 100644
--- a/ckanext/transmute/transmutators.py
+++ b/ckanext/transmute/transmutators.py
@@ -1,5 +1,5 @@
 from __future__ import annotations
-from typing import Callable, Any
+from typing import Callable, Any, Optional
 from datetime import datetime
 
 from dateutil.parser import parse, ParserError
@@ -219,21 +219,20 @@ def unique_only(field: Field) -> Field:
 
 
 @transmutator
-def mapper(field: Field, mapping: dict[Any, Any], default: Any) -> Field:
+def mapper(field: Field, mapping: dict[Any, Any], default: Optional[Any] = None) -> Field:
     """Map a value with a new value. The initial value must serve as a key within
-    a mapping dictionary, while the dic value will represent the updated value.
-
-    In cases where the key does not exist within the mapping, a default value will be employed.
+    a mapping dictionary, while the dict value will represent the updated value.
 
     Args:
         field (Field): Field object
         mapping (dict[Any, Any]): A dictionary representing the mapping of values.
         default (Any): The default value to be used when the key is not found in the mapping.
+            If the default value is not provided, the current value will be used as it.
 
     Returns:
         Field: the same Field with new value
     """
-    new_value = mapping.get(field.value, default)
+    new_value = mapping.get(field.value, default or field.value)
 
     field.value = new_value