diff --git a/mitmproxy/addons/stickycookie.py b/mitmproxy/addons/stickycookie.py
index 27d78646b..293de5654 100644
--- a/mitmproxy/addons/stickycookie.py
+++ b/mitmproxy/addons/stickycookie.py
@@ -59,7 +59,8 @@ class StickyCookie:
                         if not self.jar[dom_port_path]:
                             self.jar.pop(dom_port_path, None)
                     else:
-                        b = attrs.with_insert(0, name, value)
+                        b = attrs.copy()
+                        b.insert(0, name, value)
                         self.jar[dom_port_path][name] = b
 
     def request(self, flow):
diff --git a/mitmproxy/net/http/cookies.py b/mitmproxy/net/http/cookies.py
index 9f32fa5ee..2f99568b5 100644
--- a/mitmproxy/net/http/cookies.py
+++ b/mitmproxy/net/http/cookies.py
@@ -31,7 +31,7 @@ _cookie_params = set((
 ESCAPE = re.compile(r"([\"\\])")
 
 
-class CookieAttrs(multidict.ImmutableMultiDict):
+class CookieAttrs(multidict.MultiDict):
     @staticmethod
     def _kconv(key):
         return key.lower()
@@ -300,7 +300,7 @@ def refresh_set_cookie_header(c, delta):
         e = email.utils.parsedate_tz(attrs["expires"])
         if e:
             f = email.utils.mktime_tz(e) + delta
-            attrs = attrs.with_set_all("expires", [email.utils.formatdate(f)])
+            attrs.set_all("expires", [email.utils.formatdate(f)])
         else:
             # This can happen when the expires tag is invalid.
             # reddit.com sends a an expires tag like this: "Thu, 31 Dec
@@ -308,7 +308,7 @@ def refresh_set_cookie_header(c, delta):
             # strictly correct according to the cookie spec. Browsers
             # appear to parse this tolerantly - maybe we should too.
             # For now, we just ignore this.
-            attrs = attrs.with_delitem("expires")
+            del attrs["expires"]
 
     rv = format_set_cookie_header([(name, value, attrs)])
     if not rv:
diff --git a/mitmproxy/types/multidict.py b/mitmproxy/types/multidict.py
index d351e48b7..e02d28a9c 100644
--- a/mitmproxy/types/multidict.py
+++ b/mitmproxy/types/multidict.py
@@ -1,11 +1,6 @@
 from abc import ABCMeta, abstractmethod
 
-
-try:
-    from collections.abc import MutableMapping
-except ImportError:  # pragma: no cover
-    from collections import MutableMapping  # Workaround for Python < 3.3
-
+from collections.abc import MutableMapping
 from mitmproxy.types import serializable
 
 
@@ -227,46 +222,6 @@ class MultiDict(_MultiDict):
         return key
 
 
-class ImmutableMultiDict(MultiDict, metaclass=ABCMeta):
-    def _immutable(self, *_):
-        raise TypeError('{} objects are immutable'.format(self.__class__.__name__))
-
-    __delitem__ = set_all = insert = _immutable
-
-    def __hash__(self):
-        return hash(self.fields)
-
-    def with_delitem(self, key):
-        """
-        Returns:
-            An updated ImmutableMultiDict. The original object will not be modified.
-        """
-        ret = self.copy()
-        # FIXME: This is filthy...
-        super(ImmutableMultiDict, ret).__delitem__(key)
-        return ret
-
-    def with_set_all(self, key, values):
-        """
-        Returns:
-            An updated ImmutableMultiDict. The original object will not be modified.
-        """
-        ret = self.copy()
-        # FIXME: This is filthy...
-        super(ImmutableMultiDict, ret).set_all(key, values)
-        return ret
-
-    def with_insert(self, index, key, value):
-        """
-        Returns:
-            An updated ImmutableMultiDict. The original object will not be modified.
-        """
-        ret = self.copy()
-        # FIXME: This is filthy...
-        super(ImmutableMultiDict, ret).insert(index, key, value)
-        return ret
-
-
 class MultiDictView(_MultiDict):
     """
     The MultiDictView provides the MultiDict interface over calculated data.
diff --git a/test/mitmproxy/test_types_multidict.py b/test/mitmproxy/test_types_multidict.py
index d566905cb..cf80c05e9 100644
--- a/test/mitmproxy/test_types_multidict.py
+++ b/test/mitmproxy/test_types_multidict.py
@@ -12,10 +12,6 @@ class TMultiDict(_TMulti, multidict.MultiDict):
     pass
 
 
-class TImmutableMultiDict(_TMulti, multidict.ImmutableMultiDict):
-    pass
-
-
 class TestMultiDict:
     @staticmethod
     def _multi():
@@ -194,36 +190,6 @@ class TestMultiDict:
         assert md == md2
 
 
-class TestImmutableMultiDict:
-    def test_modify(self):
-        md = TImmutableMultiDict()
-        with tutils.raises(TypeError):
-            md["foo"] = "bar"
-
-        with tutils.raises(TypeError):
-            del md["foo"]
-
-        with tutils.raises(TypeError):
-            md.add("foo", "bar")
-
-    def test_hash(self):
-        assert hash(TImmutableMultiDict())
-
-    def test_with_delitem(self):
-        md = TImmutableMultiDict([("foo", "bar")])
-        assert md.with_delitem("foo").fields == ()
-        assert md.fields == (("foo", "bar"),)
-
-    def test_with_set_all(self):
-        md = TImmutableMultiDict()
-        assert md.with_set_all("foo", ["bar"]).fields == (("foo", "bar"),)
-        assert md.fields == ()
-
-    def test_with_insert(self):
-        md = TImmutableMultiDict()
-        assert md.with_insert(0, "foo", "bar").fields == (("foo", "bar"),)
-
-
 class TParent:
     def __init__(self):
         self.vals = tuple()