diff --git a/src/nominatim_api/v1/format_json.py b/src/nominatim_api/v1/format_json.py
index cad76cc7..9d7c3bd4 100644
--- a/src/nominatim_api/v1/format_json.py
+++ b/src/nominatim_api/v1/format_json.py
@@ -84,8 +84,9 @@ def format_base_json(results: Union[ReverseResults, SearchResults],
 
         _write_osm_id(out, result.osm_object)
 
-        out.key('lat').float(result.centroid.lat, 7).next()\
-           .key('lon').float(result.centroid.lon, 7).next()\
+        # lat and lon must be string values
+        out.keyval('lat', f"{result.centroid.lat:0.7f}")\
+           .keyval('lon', f"{result.centroid.lon:0.7f}")\
            .keyval(class_label, result.category[0])\
            .keyval('type', result.category[1])\
            .keyval('place_rank', result.rank_search)\
@@ -112,12 +113,13 @@ def format_base_json(results: Union[ReverseResults, SearchResults],
         if options.get('namedetails', False):
             out.keyval('namedetails', result.names)
 
+        # must be string values
         bbox = cl.bbox_from_result(result)
         out.key('boundingbox').start_array()\
-           .float(bbox.minlat, 7).next()\
-           .float(bbox.maxlat, 7).next()\
-           .float(bbox.minlon, 7).next()\
-           .float(bbox.maxlon, 7).next()\
+           .value(f"{bbox.minlat:0.7f}").next()\
+           .value(f"{bbox.maxlat:0.7f}").next()\
+           .value(f"{bbox.minlon:0.7f}").next()\
+           .value(f"{bbox.maxlon:0.7f}").next()\
            .end_array().next()
 
         if result.geometry:
diff --git a/test/bdd/conftest.py b/test/bdd/conftest.py
index 7827796a..6d2b0b69 100644
--- a/test/bdd/conftest.py
+++ b/test/bdd/conftest.py
@@ -150,6 +150,10 @@ def reverse_geocode_via_api(test_config_env, pytestconfig, datatable, lat, lon):
     result = APIResult('json', 'reverse', api_response.body)
     assert result.is_simple()
 
+    assert isinstance(result.result['lat'], str)
+    assert isinstance(result.result['lon'], str)
+    result.result['centroid'] = f"POINT({result.result['lon']} {result.result['lat']})"
+
     return result
 
 
@@ -159,20 +163,8 @@ def reverse_geocode_via_api_and_grid(test_config_env, pytestconfig, node_grid, d
     coords = node_grid.get(node)
     if coords is None:
         raise ValueError('Unknown node id')
-    runner = APIRunner(test_config_env, pytestconfig.option.NOMINATIM_API_ENGINE)
-    api_response = runner.run_step('reverse',
-                                   {'lat': coords[1], 'lon': coords[0]},
-                                   datatable, 'jsonv2', {})
 
-    assert api_response.status == 200
-    assert api_response.headers['content-type'] == 'application/json; charset=utf-8'
-
-    result = APIResult('json', 'reverse', api_response.body)
-    assert result.is_simple()
-
-    result.result['centroid'] = f"POINT({result.result['lon']:.7f} {result.result['lat']:.7f})"
-
-    return result
+    return reverse_geocode_via_api(test_config_env, pytestconfig, datatable, coords[1], coords[0])
 
 
 @when(step_parse(r'geocoding(?: "(?P<query>.*)")?'),
@@ -193,7 +185,9 @@ def forward_geocode_via_api(test_config_env, pytestconfig, datatable, query):
     assert not result.is_simple()
 
     for res in result.result:
-        res['centroid'] = f"POINT({res['lon']:.7f} {res['lat']:.7f})"
+        assert isinstance(res['lat'], str)
+        assert isinstance(res['lon'], str)
+        res['centroid'] = f"POINT({res['lon']} {res['lat']})"
 
     return result