diff --git a/stix2/test/v20/test_datastore_taxii.py b/stix2/test/v20/test_datastore_taxii.py
index 5e8ea69..93049ba 100644
--- a/stix2/test/v20/test_datastore_taxii.py
+++ b/stix2/test/v20/test_datastore_taxii.py
@@ -3,6 +3,7 @@ import json
 from medallion.filters.basic_filter import BasicFilter
 import pytest
 from requests.models import Response
+import six
 from taxii2client import Collection, _filter_kwargs_to_query_params
 
 import stix2
@@ -21,8 +22,8 @@ class MockTAXIICollectionEndpoint(Collection):
 
     def add_objects(self, bundle):
         self._verify_can_write()
-        if isinstance(bundle, str):
-            bundle = json.loads(bundle)
+        if isinstance(bundle, six.string_types):
+            bundle = json.loads(bundle, encoding='utf-8')
         for object in bundle.get("objects", []):
             self.objects.append(object)
 
@@ -30,7 +31,7 @@ class MockTAXIICollectionEndpoint(Collection):
         self._verify_can_read()
         query_params = _filter_kwargs_to_query_params(filter_kwargs)
         if not isinstance(query_params, dict):
-            query_params = json.loads(query_params)
+            query_params = json.loads(query_params, encoding='utf-8')
         full_filter = BasicFilter(query_params or {})
         objs = full_filter.process_filter(
             self.objects,
@@ -44,13 +45,13 @@ class MockTAXIICollectionEndpoint(Collection):
             resp.status_code = 404
             resp.raise_for_status()
 
-    def get_object(self, id, version=None):
+    def get_object(self, id, version=None, accept=''):
         self._verify_can_read()
         query_params = None
         if version:
             query_params = _filter_kwargs_to_query_params({"version": version})
         if query_params:
-            query_params = json.loads(query_params)
+            query_params = json.loads(query_params, encoding='utf-8')
         full_filter = BasicFilter(query_params or {})
         objs = full_filter.process_filter(
             self.objects,
diff --git a/stix2/test/v21/test_datastore_taxii.py b/stix2/test/v21/test_datastore_taxii.py
index 13a389e..00561de 100644
--- a/stix2/test/v21/test_datastore_taxii.py
+++ b/stix2/test/v21/test_datastore_taxii.py
@@ -3,6 +3,7 @@ import json
 from medallion.filters.basic_filter import BasicFilter
 import pytest
 from requests.models import Response
+import six
 from taxii2client import Collection, _filter_kwargs_to_query_params
 
 import stix2
@@ -21,8 +22,8 @@ class MockTAXIICollectionEndpoint(Collection):
 
     def add_objects(self, bundle):
         self._verify_can_write()
-        if isinstance(bundle, str):
-            bundle = json.loads(bundle)
+        if isinstance(bundle, six.string_types):
+            bundle = json.loads(bundle, encoding='utf-8')
         for object in bundle.get("objects", []):
             self.objects.append(object)
 
@@ -30,7 +31,7 @@ class MockTAXIICollectionEndpoint(Collection):
         self._verify_can_read()
         query_params = _filter_kwargs_to_query_params(filter_kwargs)
         if not isinstance(query_params, dict):
-            query_params = json.loads(query_params)
+            query_params = json.loads(query_params, encoding='utf-8')
         full_filter = BasicFilter(query_params or {})
         objs = full_filter.process_filter(
             self.objects,
@@ -44,13 +45,13 @@ class MockTAXIICollectionEndpoint(Collection):
             resp.status_code = 404
             resp.raise_for_status()
 
-    def get_object(self, id, version=None):
+    def get_object(self, id, version=None, accept=''):
         self._verify_can_read()
         query_params = None
         if version:
             query_params = _filter_kwargs_to_query_params({"version": version})
         if query_params:
-            query_params = json.loads(query_params)
+            query_params = json.loads(query_params, encoding='utf-8')
         full_filter = BasicFilter(query_params or {})
         objs = full_filter.process_filter(
             self.objects,