diff --git a/.circleci/config.yml b/.circleci/config.yml
index d07383b84..82bb263f9 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -70,13 +70,9 @@ workflows:
       - "oraclelinux-8":
           {}
 
-      - "nixos":
-          name: "NixOS 21.11"
-          nixpkgs: "21.11"
-
       - "nixos":
           name: "NixOS 22.11"
-          nixpkgs: "22.11"
+          nixpkgs: "21.11"
 
       - "nixos":
           name: "NixOS unstable"
diff --git a/nix/sources.json b/nix/sources.json
index bcac22174..ddf05d39d 100644
--- a/nix/sources.json
+++ b/nix/sources.json
@@ -11,18 +11,6 @@
         "url": "https://github.com/nmattia/niv/archive/5830a4dd348d77e39a0f3c4c762ff2663b602d4c.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
-    "nixpkgs-21.11": {
-        "branch": "nixos-21.11",
-        "description": "Nix Packages collection",
-        "homepage": "",
-        "owner": "NixOS",
-        "repo": "nixpkgs",
-        "rev": "838eefb4f93f2306d4614aafb9b2375f315d917f",
-        "sha256": "1bm8cmh1wx4h8b4fhbs75hjci3gcrpi7k1m1pmiy3nc0gjim9vkg",
-        "type": "tarball",
-        "url": "https://github.com/NixOS/nixpkgs/archive/838eefb4f93f2306d4614aafb9b2375f315d917f.tar.gz",
-        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
-    },
     "nixpkgs-22.11": {
         "branch": "nixos-22.11",
         "description": "Nix Packages collection",
diff --git a/nix/tahoe-lafs.nix b/nix/tahoe-lafs.nix
index 386e3adc9..11698f611 100644
--- a/nix/tahoe-lafs.nix
+++ b/nix/tahoe-lafs.nix
@@ -34,6 +34,15 @@
 # i2p extra dependencies
 , txi2p
 
+# twisted extra dependencies - if there is overlap with our dependencies we
+# have to skip them since we can't have a name in the argument set twice.
+, appdirs
+, bcrypt
+, idna
+, pyasn1
+, pyopenssl
+, service-identity
+
 # test dependencies
 , beautifulsoup4
 , fixtures
@@ -81,8 +90,9 @@ let
     six
     treq
     twisted
-    (twisted.passthru.optional-dependencies.tls)
-    (twisted.passthru.optional-dependencies.conch)
+    # Get the dependencies for the Twisted extras we depend on, too.
+    twisted.passthru.optional-dependencies.tls
+    twisted.passthru.optional-dependencies.conch
     werkzeug
     zfec
     zope_interface
diff --git a/nix/txi2p.nix b/nix/txi2p.nix
index a3a5fea3a..c6b28aad4 100644
--- a/nix/txi2p.nix
+++ b/nix/txi2p.nix
@@ -1,4 +1,9 @@
-{ fetchPypi, buildPythonPackage, parsley, twisted, unittestCheckHook }:
+{ fetchPypi
+, buildPythonPackage
+, parsley
+, twisted
+, unittestCheckHook
+}:
 buildPythonPackage rec {
   pname = "txi2p-tahoe";
   version = "0.3.7";