diff --git a/.github/workflows/run_tests.yml b/.github/workflows/run_tests.yml
index f5b50fd..eca9ed3 100644
--- a/.github/workflows/run_tests.yml
+++ b/.github/workflows/run_tests.yml
@@ -4,10 +4,11 @@ on: [push, pull_request]
 
 jobs:
   test:
-    runs-on: ubuntu-latest
+    runs-on: ${{ matrix.os }}
     strategy:
       fail-fast: false
       matrix:
+        os: [ubuntu-latest, macos-latest]
         python-version: ["3.8", "3.9", "3.10", "3.11", "3.12", "3.13", "3.14"]
 
     steps:
diff --git a/IMPROVEMENTS.md b/IMPROVEMENTS.md
index 45a807d..0bcf298 100644
--- a/IMPROVEMENTS.md
+++ b/IMPROVEMENTS.md
@@ -156,7 +156,7 @@ Acceptance criteria:
 ### Strengthen tests and CI
 
 - [x] Run CI on pull requests as well as pushes.
-- [ ] Add macOS CI because macOS is an advertised platform.
+- [x] Add macOS CI because macOS is an advertised platform.
 - [x] Fix the Unix-socket path test that currently fails on a local macOS run.
 - [ ] Replace nonexistent issue references in `xfail` markers with real tracked
   work, then remove the markers as fixes land.