diff --git a/bigframes/core/indexers.py b/bigframes/core/indexers.py
index f6ce084714..69048b6845 100644
--- a/bigframes/core/indexers.py
+++ b/bigframes/core/indexers.py
@@ -117,6 +117,18 @@ def __getitem__(
     ) -> Union[bigframes.core.scalar.Scalar, bigframes.series.Series]:
         return self._series.loc[key]
 
+    def __setitem__(
+        self,
+        key: LocSingleKey,
+        value: bigframes.core.scalar.Scalar,
+    ):
+        if not pd.api.types.is_scalar(value):
+            raise NotImplementedError(
+                "series.at.__setitem__ only supports scalar right-hand values. "
+                f"{constants.FEEDBACK_LINK}"
+            )
+        self._series.loc[key] = value
+
 
 class LocDataFrameIndexer:
     def __init__(self, dataframe: bigframes.dataframe.DataFrame):
diff --git a/tests/system/small/test_series.py b/tests/system/small/test_series.py
index 183ba01c0e..c8bd0f7afd 100644
--- a/tests/system/small/test_series.py
+++ b/tests/system/small/test_series.py
@@ -1012,6 +1012,17 @@ def test_loc_setitem_cell(scalars_df_index, scalars_pandas_df_index):
     pd.testing.assert_series_equal(bf_original.to_pandas(), pd_original)
 
 
+def test_at_setitem_row_label_scalar(scalars_dfs):
+    scalars_df, scalars_pandas_df = scalars_dfs
+    bf_series = scalars_df["int64_col"]
+    pd_series = scalars_pandas_df["int64_col"].copy()
+    bf_series.at[1] = 1000
+    pd_series.at[1] = 1000
+    bf_result = bf_series.to_pandas()
+    pd_result = pd_series.astype("Int64")
+    pd.testing.assert_series_equal(bf_result, pd_result)
+
+
 def test_ne_obj_series(scalars_dfs):
     scalars_df, scalars_pandas_df = scalars_dfs
     col_name = "string_col"