diff --git a/nixos/modules/pspkgs.nix b/nixos/modules/pspkgs.nix
index 851f4e71783c3c1dcc9fc596b37722866fef7331..11ef89929ef0ad20f3c5f7795554a90085ed66f9 100644
--- a/nixos/modules/pspkgs.nix
+++ b/nixos/modules/pspkgs.nix
@@ -4,7 +4,16 @@
 { pkgs }:
 import pkgs.path {
   overlays = [
-    (import ./zkap-overlay.nix)
+    # For some reason the order of these overlays matters.  Maybe it has to do
+    # with our python27 override, I'm not sure.  In the other order, we end up
+    # with two derivations of each of Twisted and treq which conflict with
+    # each other.
     (import ./overlays.nix)
+    # It might be nice to eventually remove this.  ZKAPAuthorizer now
+    # self-applies this overlay without our help.  We only still have it
+    # because it also defines tahoe-lafs which we want to use.  We can't see
+    # tahoe-lafs from the self-applied overlay because that overlay is applied
+    # to ZKAPAuthorizer's nixpkgs, not to the one we're using.
+    (import ./zkap-overlay.nix)
   ];
 }
diff --git a/nixos/pkgs/zkapissuer-repo.nix b/nixos/pkgs/zkapissuer-repo.nix
index 9ea985499378b2773537dd09cbdd651f9a90d6f0..66d3bf2f1078ab997fcf51ecc64260e9cab74f21 100644
--- a/nixos/pkgs/zkapissuer-repo.nix
+++ b/nixos/pkgs/zkapissuer-repo.nix
@@ -4,6 +4,6 @@ in
   pkgs.fetchFromGitHub {
     owner = "PrivateStorageio";
     repo = "PaymentServer";
-    rev = "d7ba9ffd970d7b4caa99ba93433f613d4773b17c";
-    sha256 = "0h086173m6ih24wmdy7jshwv7ihl17wh7qir2x4slwydhyrfrwjk";
+    rev = "d6ad0042842ca0501c1e378b19bfdb42d5644223";
+    sha256 = "018ybp83ljdwjn2kv1smkb5rx5h0hgw17a452bsyxdq61ysv4ajv";
   }
\ No newline at end of file