diff --git a/pcmdi_metrics/mean_climate/lib/create_mean_climate_parser.py b/pcmdi_metrics/mean_climate/lib/create_mean_climate_parser.py
index ab5861051..02719bd73 100644
--- a/pcmdi_metrics/mean_climate/lib/create_mean_climate_parser.py
+++ b/pcmdi_metrics/mean_climate/lib/create_mean_climate_parser.py
@@ -186,6 +186,7 @@ def create_mean_climate_parser():
         dest="custom_observations",
         help="Path to an alternative, custom observation file",
         required=False,
+        default=""
     )
 
     parser.add_argument(
diff --git a/pcmdi_metrics/mean_climate/mean_climate_driver.py b/pcmdi_metrics/mean_climate/mean_climate_driver.py
index 3eac17b48..a489be9dc 100755
--- a/pcmdi_metrics/mean_climate/mean_climate_driver.py
+++ b/pcmdi_metrics/mean_climate/mean_climate_driver.py
@@ -46,6 +46,7 @@
 reference_data_path = parameter.reference_data_path
 metrics_output_path = parameter.metrics_output_path
 diagnostics_output_path = parameter.diagnostics_output_path
+custom_obs = parameter.custom_observations
 debug = parameter.debug
 cmec = parameter.cmec
 
@@ -122,8 +123,11 @@
 
 # load obs catalogue json
 egg_pth = resources.resource_path()
-obs_file_name = "obs_info_dictionary.json"
-obs_file_path = os.path.join(egg_pth, obs_file_name)
+if len(custom_obs) > 0:
+    obs_file_path = custom_obs
+else:
+    obs_file_name = "obs_info_dictionary.json"
+    obs_file_path = os.path.join(egg_pth, obs_file_name)
 with open(obs_file_path) as fo:
     obs_dict = json.loads(fo.read())
 # if debug: