diff --git a/vcr/request.py b/vcr/request.py
index 5415743..10b9fb5 100644
--- a/vcr/request.py
+++ b/vcr/request.py
@@ -7,13 +7,10 @@ class Request(object):
         self.method = method
         self.uri = uri
         self.body = body
-        # make headers a frozenset so it will be hashable
-        self.headers = frozenset(headers.items())
+        self.headers = headers
 
     def add_header(self, key, value):
-        tmp = dict(self.headers)
-        tmp[key] = value
-        self.headers = frozenset(tmp.iteritems())
+        self.headers[key] = value
 
     @property
     def scheme(self):
diff --git a/vcr/serializers/jsonserializer.py b/vcr/serializers/jsonserializer.py
index eeaa91b..2dcfa09 100644
--- a/vcr/serializers/jsonserializer.py
+++ b/vcr/serializers/jsonserializer.py
@@ -6,12 +6,6 @@ except ImportError:
     import json
 
 
-def _json_default(obj):
-    if isinstance(obj, frozenset):
-        return dict(obj)
-    return obj
-
-
 def deserialize(cassette_string):
     data = json.loads(cassette_string)
     requests = [Request._from_dict(r['request']) for r in data]
@@ -28,8 +22,8 @@ def serialize(cassette_dict):
         cassette_dict['responses']
     )])
     try:
-        return json.dumps(data, indent=4, default=_json_default)
-    except UnicodeDecodeError as e:
+        return json.dumps(data, indent=4)
+    except UnicodeDecodeError:
         raise UnicodeDecodeError(
             "Error serializing cassette to JSON. ",
             "Does this HTTP interaction contain binary data? ",