diff --git a/.circleci/config.yml b/.circleci/config.yml
index 9a959ae8a6d580596c1d515defcdc1245d246d18..24d4a4521c5777ef221e14aac185bdda94584a8b 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -144,17 +144,11 @@ jobs:
       # CACHIX_AUTH_TOKEN is manually set in the CircleCI web UI and allows us to push to CACHIX_NAME.
       CACHIX_NAME: "privatestorage-opensource"
 
-      # Specify a revision of PrivateStorageio/nixpkgs to run against.  This
-      # essentially pins the majority of the software involved in the build.
-      # This revision is selected arbitrarily (it's just new enough to define
-      # all of the PrivateStorage stuff that ZKAPAuthorizer depends on).  It's
-      # somewhat current as of the time of this comment.  We can bump it to a
-      # newer version when that makes sense.  Meanwhile, the platform won't
-      # shift around beneath us unexpectedly.
-      NIX_PATH: "nixpkgs=https://github.com/PrivateStorageio/nixpkgs/archive/730129887a84a8f84f3b78ffac7add72aeb551b6.tar.gz"
 
     steps:
       - run:
+          environment:
+            NIX_PATH: "nixpkgs=https://nixos.org/channels/nixos-21.05-small"
           name: "Set up Cachix"
           command: |
             nix-env -iA nixpkgs.cachix
@@ -163,6 +157,16 @@ jobs:
       - "checkout"
 
       - run:
+          environment:
+            # Specify a revision of PrivateStorageio/nixpkgs to run against.
+            # This essentially pins the majority of the software involved in
+            # the build.  This revision is selected arbitrarily (it's just new
+            # enough to define all of the PrivateStorage stuff that
+            # ZKAPAuthorizer depends on).  It's somewhat current as of the
+            # time of this comment.  We can bump it to a newer version when
+            # that makes sense.  Meanwhile, the platform won't shift around
+            # beneath us unexpectedly.
+            NIX_PATH: "nixpkgs=https://github.com/PrivateStorageio/nixpkgs/archive/730129887a84a8f84f3b78ffac7add72aeb551b6.tar.gz"
           name: "Run Test Suite"
           command: |
             # Building the package has, as a side effect, running the test