diff --git a/bigframes/_config/bigquery_options.py b/bigframes/_config/bigquery_options.py
index 09ffee95d4..648b69dea7 100644
--- a/bigframes/_config/bigquery_options.py
+++ b/bigframes/_config/bigquery_options.py
@@ -171,7 +171,7 @@ def location(self) -> Optional[str]:
 
     @location.setter
     def location(self, value: Optional[str]):
-        if self._session_started and self._location != value:
+        if self._session_started and self._location != _get_validated_location(value):
             raise ValueError(SESSION_STARTED_MESSAGE.format(attribute="location"))
         self._location = _get_validated_location(value)
 
diff --git a/tests/unit/_config/test_bigquery_options.py b/tests/unit/_config/test_bigquery_options.py
index 686499aa75..3c80f00a37 100644
--- a/tests/unit/_config/test_bigquery_options.py
+++ b/tests/unit/_config/test_bigquery_options.py
@@ -58,6 +58,18 @@ def test_setter_raises_if_session_started(attribute, original_value, new_value):
     assert getattr(options, attribute) is not new_value
 
 
+def test_location_set_us_twice():
+    """This test ensures the fix for b/423220936 is working as expected."""
+    options = bigquery_options.BigQueryOptions()
+    setattr(options, "location", "us")
+    assert getattr(options, "location") == "US"
+
+    options._session_started = True
+
+    setattr(options, "location", "us")
+    assert getattr(options, "location") == "US"
+
+
 @pytest.mark.parametrize(
     [
         "attribute",