diff --git a/python/python/lancedb/merge.py b/python/python/lancedb/merge.py
index 3debed97b..115a47e2d 100644
--- a/python/python/lancedb/merge.py
+++ b/python/python/lancedb/merge.py
@@ -92,8 +92,10 @@ class LanceMergeInsertBuilder(object):
         self._when_not_matched_by_source_delete = True
         if isinstance(condition, Expr):
             self._when_not_matched_by_source_condition_expr = condition._inner
-        elif condition is not None:
+            self._when_not_matched_by_source_condition = None
+        else:
             self._when_not_matched_by_source_condition = condition
+            self._when_not_matched_by_source_condition_expr = None
         return self
 
     def use_index(self, use_index: bool) -> LanceMergeInsertBuilder:
diff --git a/python/python/tests/test_table.py b/python/python/tests/test_table.py
index a355cf101..542c944c8 100644
--- a/python/python/tests/test_table.py
+++ b/python/python/tests/test_table.py
@@ -2364,6 +2364,29 @@ def test_merge_insert_by_source_delete_expr(mem_db: DBConnection):
     assert table.to_arrow().sort_by("a") == expected
 
 
+def test_merge_insert_by_source_delete_reconfigure(mem_db: DBConnection):
+    # Calling when_not_matched_by_source_delete() again with no condition must
+    # widen the delete to unconditional, not keep the earlier condition around.
+    table = mem_db.create_table(
+        "my_table",
+        data=pa.table({"a": [1, 2, 3], "b": ["a", "b", "c"]}),
+    )
+    new_data = pa.table({"a": [2, 4], "b": ["x", "z"]})
+
+    merge_insert_res = (
+        table.merge_insert("a")
+        .when_matched_update_all()
+        .when_not_matched_insert_all()
+        .when_not_matched_by_source_delete("a > 2")
+        .when_not_matched_by_source_delete()
+        .execute(new_data)
+    )
+    assert merge_insert_res.num_deleted_rows == 2
+
+    expected = pa.table({"a": [2, 4], "b": ["x", "z"]})
+    assert table.to_arrow().sort_by("a") == expected
+
+
 @pytest.mark.asyncio
 async def test_merge_insert_by_source_delete_expr_async(
     mem_db_async: AsyncConnection,