diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 8850430..ceec429 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -67,9 +67,8 @@ jobs:
         pip3 install -r requirements-dev.txt
         pip3 install -r requirements-provider.txt
         python3 setup.py install
+        pip3 install --upgrade numpy
         #pip3 install --upgrade rasterio==1.1.8
-    - name: run flake8 ⚙️
-      run: find . -type f -name "*.py" | xargs flake8
     - name: setup test data ⚙️
       run: |
         python3 tests/load_es_data.py tests/data/ne_110m_populated_places_simple.geojson geonameid
@@ -106,6 +105,8 @@ jobs:
         pytest tests/test_util.py
         pytest tests/test_xarray_netcdf_provider.py
         pytest tests/test_xarray_zarr_provider.py
+    - name: run flake8 ⚙️
+      run: find . -type f -name "*.py" | xargs flake8
     - name: build docs 🏗️
       run: cd docs && make html
     - name: failed tests 🚩
diff --git a/pygeoapi/provider/xarray_.py b/pygeoapi/provider/xarray_.py
index 64b1cc1..e80a353 100644
--- a/pygeoapi/provider/xarray_.py
+++ b/pygeoapi/provider/xarray_.py
@@ -556,9 +556,15 @@ def _to_datetime_string(datetime_obj):
 
     try:
         value = np.datetime_as_string(datetime_obj)
+    except TypeError as err:
+        LOGGER.warning(err)
+        if datetime_obj.microsecond != 0:
+            value = datetime_obj.strftime('%Y-%m-%dT%H:%M:%S.%fZ')
+        else:
+            value = datetime_obj.strftime('%Y-%m-%dT%H:%M:%SZ')
     except Exception as err:
         LOGGER.warning(err)
-        value = datetime_obj.strftime('%Y-%m-%dT%H:%M:%S.%fZ')
+        raise RuntimeError(err)
 
     return value