diff --git a/CHANGELOG.md b/CHANGELOG.md
index f50855592..b86bd3fc6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -12,9 +12,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Changed
 - The bundled Data Contract Editor (`datacontract edit`) is updated to 0.1.16
+- `datacontract lint` and `datacontract test`: reject duplicate keys in a data contract instead of silently keeping the last value (#1741 @kamathramu87)
 
 ### Fixed
-- `datacontract export sql`: apostrophes and backslashes in descriptions no longer break ClickHouse and Snowflake `COMMENT` clauses (#1729)
+- `datacontract export sql`: apostrophes and backslashes in descriptions no longer break ClickHouse and Snowflake `COMMENT` clauses (#1729,#1731 @banshee @ezno12)
 
 ## [1.2.7] - 2026-10-16
 
diff --git a/datacontract/lint/resolve.py b/datacontract/lint/resolve.py
index 884f18628..121df3795 100644
--- a/datacontract/lint/resolve.py
+++ b/datacontract/lint/resolve.py
@@ -54,7 +54,26 @@ class _LaxOpenDataContractStandard(OpenDataContractStandard):
 class _SafeLoaderNoTimestamp(yaml.SafeLoader):
     """SafeLoader that keeps dates/timestamps as strings instead of converting to datetime objects."""
 
-    pass
+    def construct_mapping(self, node: yaml.MappingNode, deep: bool = False) -> dict[object, object]:
+        # Skip merge keys: overriding a value inherited from an anchor is valid YAML.
+        first_marks = {}
+        for key_node, _ in node.value:
+            if key_node.tag == "tag:yaml.org,2002:merge":
+                continue
+            key = self.construct_object(key_node, deep=deep)
+            try:
+                first_mark = first_marks.get(key)
+            except TypeError:
+                return super().construct_mapping(node, deep=deep)
+            if first_mark is not None:
+                raise yaml.constructor.ConstructorError(
+                    f"found key {key!r}",
+                    first_mark,
+                    f"found duplicate key {key!r}",
+                    key_node.start_mark,
+                )
+            first_marks[key] = key_node.start_mark
+        return super().construct_mapping(node, deep=deep)
 
 
 # Remove the timestamp implicit resolver so dates like 2022-01-15 stay as strings
diff --git a/tests/test_resolve.py b/tests/test_resolve.py
index ab75d134d..a81ebe659 100644
--- a/tests/test_resolve.py
+++ b/tests/test_resolve.py
@@ -1,6 +1,10 @@
 import tempfile
 
-from datacontract.lint.resolve import resolve_data_contract
+import pytest
+
+from datacontract.data_contract import DataContract
+from datacontract.lint.resolve import _to_yaml, resolve_data_contract
+from datacontract.model.exceptions import DataContractException
 from datacontract.model.server import get_server_type
 
 # logging.basicConfig(level=logging.INFO, force=True)
@@ -313,3 +317,47 @@ def test_resolve_dcs_status_preserved_when_set():
     """,
     )
     assert odcs.status == "active"
+
+
+@pytest.mark.parametrize(
+    "document",
+    [
+        "status: active\nstatus: draft\n",
+        "schema:\n- name: orders\n  properties:\n  - name: id\n    required: true\n    required: false\n",
+        "schema:\n- name: orders\n  quality: {type: sql, query: SELECT 1, query: SELECT 2}\n",
+    ],
+)
+def test_duplicate_mapping_keys_are_rejected(document: str) -> None:
+    with pytest.raises(DataContractException, match="duplicate key"):
+        _to_yaml(document)
+
+
+def test_duplicate_key_error_identifies_source_and_line() -> None:
+    with pytest.raises(DataContractException) as exc:
+        _to_yaml("apiVersion: v3.2.0\nversion: 1.0.0\nversion: 2.0.0\n", "contracts/orders.yaml")
+    assert "contracts/orders.yaml" in str(exc.value)
+    assert "line 2" in str(exc.value)
+    assert "line 3" in str(exc.value)
+    assert "line 1" not in str(exc.value)
+
+
+def test_yaml_merge_allows_explicit_override() -> None:
+    parsed = _to_yaml("defaults: &defaults {required: false}\ncolumn: {<<: *defaults, required: true}\n")
+    assert parsed["column"]["required"] is True
+
+
+def test_yaml_merge_does_not_hide_duplicate_explicit_keys() -> None:
+    with pytest.raises(DataContractException, match="duplicate key"):
+        _to_yaml("defaults: &defaults {required: false}\ncolumn: {<<: *defaults, required: true, required: false}\n")
+
+
+def test_date_strings_and_distinct_mapping_keys_are_unchanged() -> None:
+    parsed = _to_yaml("date: 2026-10-13\nfirst: {name: id}\nsecond: {name: id}\n")
+    assert parsed["date"] == "2026-10-13"
+    assert parsed["first"] == parsed["second"] == {"name": "id"}
+
+
+def test_lint_reports_duplicate_keys_as_a_failed_check() -> None:
+    run = DataContract(data_contract_str="apiVersion: v3.0.2\napiVersion: v3.2.0\n").lint()
+    assert not run.has_passed()
+    assert any("duplicate key" in (check.reason or "") for check in run.checks)