diff --git a/app/main/lib/text_similarity.py b/app/main/lib/text_similarity.py
index ff37f6ce..1a62afa8 100644
--- a/app/main/lib/text_similarity.py
+++ b/app/main/lib/text_similarity.py
@@ -201,13 +201,24 @@ def strip_vectors(results):
     return results
 
 def restrict_results(results, search_params, model_key):
+    """
+    min_es_score is the minimum elasticsearch score needed to include a result. 
+    This is applied after the results are retrieved from Elasticsearch.  
+    The threshold parameter is in the range [0,1] and used when making the query. 
+    The min_es_score is used after results are retrieved and applied to the 
+    Elasticsearch scores, which are in the range [0, +Inf]. 
+    """
     out_results = []
-    try:
-        min_es_score = float(search_params.get("min_es_score"))
-    except (ValueError, TypeError) as e:
-        app.logger.info(f"search_params failed on min_es_score for {search_params}, raised error as {e}")
-        min_es_score = None
+    min_es_score = search_params.get("min_es_score")
+    if min_es_score is None:
+        min_es_score = 0.0
+        app.logger.warning(f"min_es_score is missing or None, defaulting to {min_es_score}")
     if min_es_score is not None and model_key == "elasticsearch":
+        try:
+            min_es_score = float(min_es_score)
+        except ValueError as e:
+            app.logger.error(f"Invalid min_es_score '{min_es_score}': {e}")
+            raise(e)
         for result in results:
             if "_score" in result and min_es_score < result["_score"]:
                 out_results.append(result)
diff --git a/app/test/test_similarity.py b/app/test/test_similarity.py
index c149af19..cec2787d 100644
--- a/app/test/test_similarity.py
+++ b/app/test/test_similarity.py
@@ -589,8 +589,9 @@ def test_model_similarity_with_vector(self):
 
 
     def test_min_es_search(self):
+        # confirm that min es filtering works
         with self.client:
-            data={
+            data = {
                 'text':'min_es_score',
                 'models':['elasticsearch'],
             }
@@ -609,7 +610,7 @@ def test_min_es_search(self):
             result = json.loads(response.data.decode())
 
             self.assertEqual(1, len(result['result']))
-            data['min_es_score']=10+result['result'][0]['score']
+            data['min_es_score'] = 10+result['result'][0]['score']
 
             response = self.client.post(
                 '/text/similarity/search/',
@@ -619,5 +620,29 @@ def test_min_es_search(self):
             result = json.loads(response.data.decode())
             self.assertEqual(0, len(result['result']))
 
+            # confirm that min_es_score missing or None: set to zero  with warning
+            data['min_es_score'] = None
+            response2 = self.client.post(
+                '/text/similarity/search/',
+                data=json.dumps(data),
+                content_type='application/json'
+            )
+            result2 = json.loads(response2.data.decode())
+            self.assertEqual(1, len(result2['result']))
+
+            # confirm that min_es_score cannot parse as float: log error and raise exception?
+            # we won't see exception here, but result should not be sucess
+            data['min_es_score'] = 'fifty'
+            response = self.client.post(
+                '/text/similarity/search/',
+                data=json.dumps(data),
+                content_type='application/json'
+            )
+            assert response.status_code == 500, f"status code was{response.status_code}"
+            result = json.loads(response.data.decode())
+            self.assertIsNone(result.get('success')), f"result was {result}"
+            # TODO: is excption being swollowed? Need to confirm logging
+            
+
 if __name__ == '__main__':
     unittest.main()
\ No newline at end of file