diff --git a/new.nix b/new.nix
index 3974dae3ecc8a6be0fb3c5a9d2c2c122b96f0b6e..c8db100db4fde872c1a057dd24899cc362ab3acb 100644
--- a/new.nix
+++ b/new.nix
@@ -9,6 +9,7 @@ in
   let
     providers = {
       _default = "sdist,nixpkgs,wheel";
+      tahoe-lafs = "nixpkgs";
       # not packaged in nixpkgs at all, we can use the binary wheel from
       # pypi though.
       python-challenge-bypass-ristretto = "wheel";
@@ -26,30 +27,49 @@ in
     tahoe-versions = {
       "1.14.0" = {
         requirements = builtins.readFile ./requirements/base.txt;
-        propagatedBuildInputs = [];
+        overridesPre = [];
+        _.tahoe-lafs.patches = [
+          (
+            pkgs.fetchpatch {
+              url = "https://raw.githubusercontent.com/PrivateStorageio/nixpkgs/privatestorageio/pkgs/development/python-modules/tahoe-lafs/rsa-exponent.patch";
+              sha256 = "sha256-0vIMj5gZPbKLkow6wpA+Tz7bpyy+mZRSSFGmpg0VMyk=";
+            }
+          )
+        ];
       };
       "1.16.0rc1" = rec {
         requirements = builtins.readFile ./requirements/base-1.16.txt;
-        propagatedBuildInputs = [
+        _ = {};
+        overridesPre = [
           (
-            mach-nix.buildPythonPackage {
-              python = "python27";
-              pname = "tahoe-lafs";
-              version = "1.16.0rc1";
-              inherit requirements providers;
-              postPatch = ''
-                cat > src/allmydata/_version.py <<EOF
-                # This _version.py is generated by nix.
+            self: super: {
+              tahoe-lafs = mach-nix.buildPythonPackage {
+                python = "python27";
+                pname = "tahoe-lafs";
+                version = "1.16.0rc1";
+                inherit providers;
+                #inherit requirements providers;
+                # See https://github.com/DavHau/mach-nix/issues/190
+                requirementsExtra = ''
+                  pyrsistent
+                  foolscap == 0.13.1
+                  configparser
+                  eliot
+                  '';
+                postPatch = ''
+                  cat > src/allmydata/_version.py <<EOF
+                  # This _version.py is generated by nix.
 
-                verstr = "$version"
-                __version__ = verstr
-                EOF
+                  verstr = "$version"
+                  __version__ = verstr
+                  EOF
                 '';
-              src = pkgs.fetchFromGitHub {
-                owner = "fenn-cs";
-                repo = "tahoe-lafs";
-                rev = "f6a96ae3976ee21ad0376f7b6a22fc3d12110dce";
-                sha256 = "ZN2V5vH+VqPaBmQXXqyH+vUiqW1YNhz+7LsiNNhA/4g=";
+                src = pkgs.fetchFromGitHub {
+                  owner = "fenn-cs";
+                  repo = "tahoe-lafs";
+                  rev = "f6a96ae3976ee21ad0376f7b6a22fc3d12110dce";
+                  sha256 = "ZN2V5vH+VqPaBmQXXqyH+vUiqW1YNhz+7LsiNNhA/4g=";
+                };
               };
             }
           )
@@ -57,24 +77,16 @@ in
       };
     };
   in
-#    (builtins.elemAt tahoe-versions."1.16.0rc1".propagatedBuildInputs 0)
-#/*
-  mach-nix.buildPythonApplication rec {
-    python = "python27";
-    name = "zero-knowledge-access-pass-authorizer";
-    src = ./.;
-    inherit providers;
-    inherit (tahoe-versions.${tahoe-lafs}) requirements propagatedBuildInputs;
-    _.tahoe-lafs.patches = [
-      (
-        pkgs.fetchpatch {
-          url = "https://raw.githubusercontent.com/PrivateStorageio/nixpkgs/privatestorageio/pkgs/development/python-modules/tahoe-lafs/rsa-exponent.patch";
-          sha256 = "sha256-0vIMj5gZPbKLkow6wpA+Tz7bpyy+mZRSSFGmpg0VMyk=";
-        }
-      )
-    ];
-    format = "setuptools";
-    # Record some settings here, so downstream nix files can consume them.
-    meta.mach-nix = { inherit python providers; };
-  }
-  /**/
+    #    (builtins.elemAt tahoe-versions."1.16.0rc1".propagatedBuildInputs 0)
+    #/*
+    mach-nix.buildPythonApplication rec {
+      python = "python27";
+      name = "zero-knowledge-access-pass-authorizer";
+      src = ./.;
+      inherit providers;
+      inherit (tahoe-versions.${tahoe-lafs}) requirements overridesPre _;
+      format = "setuptools";
+      # Record some settings here, so downstream nix files can consume them.
+      meta.mach-nix = { inherit python providers; };
+    }
+/**/
diff --git a/requirements/base-1.16.txt b/requirements/base-1.16.txt
index ef84c2b7aa0fbe1e500c0bf70f880507afb03534..bcece6ed42c7bc870af9ba277ba487f8322d6dab 100644
--- a/requirements/base-1.16.txt
+++ b/requirements/base-1.16.txt
@@ -115,6 +115,7 @@ pyopenssl==21.0.0
     # via
     #   foolscap
     #   twisted
+tahoe-lafs
 pyrsistent==0.16.1
     # via
     #   eliot