diff --git a/ate/response.py b/ate/response.py
index d46a57fd..83caedb9 100644
--- a/ate/response.py
+++ b/ate/response.py
@@ -89,13 +89,14 @@ class ResponseObject(object):
             try:
                 value = variables_mapping[validator_key]
                 validator_dict["value"] = value
+                expected_value = validator_dict["expected"]
             except KeyError:
                 raise exception.ParamsError("invalid validator %s" % validator_key)
 
             match_expected = utils.match_expected(
                 value,
-                validator_dict["expected"],
-                validator_dict["comparator"]
+                expected_value,
+                validator_dict.get("comparator", "eq")
             )
 
             if not match_expected:
diff --git a/test/test_response.py b/test/test_response.py
index 73ba023b..c4d02723 100644
--- a/test/test_response.py
+++ b/test/test_response.py
@@ -182,3 +182,31 @@ class TestResponse(ApiServerUnittest):
         diff_content_dict = resp_obj.validate(validators, variables_mapping)
         self.assertTrue(resp_obj.success)
         self.assertEqual(diff_content_dict, {})
+
+    def test_validate_exception(self):
+        url = "http://127.0.0.1:5000/"
+        resp = requests.get(url)
+        resp_obj = response.ResponseObject(resp)
+
+        # expected value missed in validators
+        validators = {
+            "resp_status_code": {"comparator": "eq", "expected": 201},
+            "resp_body_success": {"comparator": "eq"}
+        }
+        variables_mapping = {
+            "resp_status_code": 200,
+            "resp_body_success": True
+        }
+        with self.assertRaises(exception.ParamsError):
+            resp_obj.validate(validators, variables_mapping)
+
+        # expected value missed in validators
+        validators = {
+            "resp_status_code": {"comparator": "eq", "expected": 201},
+            "resp_body_success": {"comparator": "eq", "expected": True}
+        }
+        variables_mapping = {
+            "resp_status_code": 200
+        }
+        with self.assertRaises(exception.ParamsError):
+            resp_obj.validate(validators, variables_mapping)