diff --git a/appveyor.yml b/appveyor.yml
index c9502e81..0f57bbfa 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -10,6 +10,10 @@ configuration:
   - Release
 environment:
   ARCH: amd64
+  # Hunter 0.24.0's CMake scripts declare a minimum version below 3.5, which
+  # CMake >= 4 rejects. The environment variable (unlike -D) also reaches
+  # Hunter's child cmake invocations. Ignored by CMake < 4.
+  CMAKE_POLICY_VERSION_MINIMUM: 3.5
   matrix:
     - VS: 2019
       APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2019
diff --git a/circle.yml b/circle.yml
index 2054c6d8..18674b7c 100644
--- a/circle.yml
+++ b/circle.yml
@@ -276,7 +276,17 @@ jobs:
       - test-python-package
       - run:
           name: "Build wheels"
-          command: sh scripts/ci/python_build_wheels.sh
+          # Build a universal2 (x86_64 + arm64) wheel. The architecture flags
+          # must reach both the cmake build of the static libraries and the
+          # cffi extension build.
+          command: |
+            export MACOSX_DEPLOYMENT_TARGET=11.0
+            export CMAKE_OSX_ARCHITECTURES="arm64;x86_64"
+            export ARCHFLAGS="-arch arm64 -arch x86_64"
+            export CFLAGS="-arch arm64 -arch x86_64"
+            export LDFLAGS="-arch arm64 -arch x86_64"
+            export _PYTHON_HOST_PLATFORM="macosx-11.0-universal2"
+            sh scripts/ci/python_build_wheels.sh
       - store_artifacts:
           path: ~/project/dist
           destination: dist