diff --git a/.github/workflows/mac_os.yml b/.github/workflows/mac-os.yml
similarity index 78%
rename from .github/workflows/mac_os.yml
rename to .github/workflows/mac-os.yml
index 79bb1f2..c813ace 100644
--- a/.github/workflows/mac_os.yml
+++ b/.github/workflows/mac-os.yml
@@ -2,14 +2,9 @@
 
 name: ci-mac-os
 
-# We want to run CI on all pull requests. Additionally, Bors needs workflows to
-# run on the `staging` and `trying` branches.
-on:
-  pull_request:
-  push:
-    branches:
-      - staging
-      - trying
+# We run this workflow during pull request review, but not for Bors merges, as
+# it takes over an hour to run.
+on: pull_request
 
 jobs:
   ci-mac-os:
diff --git a/bors.toml b/bors.toml
index dfae601..4b9b851 100644
--- a/bors.toml
+++ b/bors.toml
@@ -1,5 +1,4 @@
 status = [
   "ci",
-  "ci-mac-os",
   "size-diff",
 ]