diff --git a/tests/extract/test_incremental.py b/tests/extract/test_incremental.py
index 2599a442db..578d5b2e0c 100644
--- a/tests/extract/test_incremental.py
+++ b/tests/extract/test_incremental.py
@@ -2706,3 +2706,50 @@ def some_data():
         "created_at"
     ]
     assert s["last_value"] == 2
+
+
+@pytest.mark.parametrize("item_type", ALL_TEST_DATA_ITEM_FORMATS)
+def test_deduplication_on_write_disposition_not_merge(
+    item_type: TestDataItemFormat,
+) -> None:
+    if item_type in ["pandas", "arrow-table", "arrow-batch"]:
+        os.environ["NORMALIZE__PARQUET_NORMALIZER__ADD_DLT_LOAD_ID"] = "True"
+
+    @dlt.resource(write_disposition="replace", merge_key="id", primary_key="id")
+    def some_data(
+        created_at=dlt.sources.incremental("created_at"),
+    ):
+        yield data_to_item_format(
+            item_type,
+            [
+                {"id": 1, "created_at": 1},
+                {"id": 2, "created_at": 2},
+            ],
+        )
+
+    p = dlt.pipeline(pipeline_name=uniq_id())
+    load_info = p.run(some_data(), destination="duckdb")
+    assert len(load_info.loads_ids) == 1
+    load_id_1 = load_info.loads_ids[0]
+
+    load_info_2 = p.run(some_data(), destination="duckdb")
+    load_id_2 = load_info_2.loads_ids[0]
+    assert load_id_1 != load_id_2
+
+    with p.sql_client() as client:
+        assert_query_data(p, "select id from some_data order by id", [1, 2])
+
+        # no duplicates
+        assert_query_data(p, "select id from some_data order by id", [1, 2])
+
+        load_ids = client.execute_sql("select _dlt_load_id from some_data")
+        assert len(set(load_ids)) == 1, "Expected only a single load in the destination"
+        assert load_id_2 == load_ids[0][0]
+
+        # row with id=2 got updated – even though it has the same merge_key as the first row with id=2
+        assert load_id_1 != load_ids[0][0], "Expected only the second load in the destination"
+
+    s = p.state["sources"][p.default_schema_name]["resources"]["some_data"]["incremental"][
+        "created_at"
+    ]
+    assert s["last_value"] == 2