diff --git a/.github/workflows/composer-compatibility.yml b/.github/workflows/composer-compatibility.yml
index 9c9f9ea98..6014cf7ce 100644
--- a/.github/workflows/composer-compatibility.yml
+++ b/.github/workflows/composer-compatibility.yml
@@ -181,7 +181,10 @@ jobs:
         include:
           - {os: macos-latest, composer: '1.10.28', php: '8.1', sha256: 0915af36eb01e3f0e16cd309adff7051832b9ef014e38371756804b20425cd5a}
           - {os: macos-latest, composer: '2.2.30', php: '8.3', sha256: 8c2b4478b64f8f7cdf1574838fdb0033b29049ca821dad452db7a3dcfcdbffc2}
-          - {os: macos-latest, composer: '2.10.3', php: '8.5', sha256: 7a2d379d5b8ffdaa028580ef26494c36d2feef4b178d3dd1473a4dbc5e17c8d6}
+          # PHP 8.4 on macOS: setup-php 2.37.2 cannot install 8.5 from Homebrew
+          # since PHP 8.6 shipped (every run from 2026-10-07 23:51Z failed in
+          # "Setup PHP"). Ubuntu and Windows keep the 2.10.3 / 8.5 cell.
+          - {os: macos-latest, composer: '2.10.3', php: '8.4', sha256: 7a2d379d5b8ffdaa028580ef26494c36d2feef4b178d3dd1473a4dbc5e17c8d6}
     runs-on: ${{ matrix.os }}
     timeout-minutes: 60
     steps: *native-steps
diff --git a/docs/testing/composer-compatibility.md b/docs/testing/composer-compatibility.md
index 9347d8e7b..afaa6f30d 100644
--- a/docs/testing/composer-compatibility.md
+++ b/docs/testing/composer-compatibility.md
@@ -43,7 +43,7 @@ vendored (`e2e_vendor_composer_build`) and hosted
 | --- | --- |
 | Ubuntu | 1.10.28 (8.1), 2.0.14 (8.0), 2.1.14 (8.1), 2.2.30 (8.1, 8.3), 2.5.8 (8.2), 2.8.12 (8.4), 2.9.8 (8.4), 2.10.3 (8.5) |
 | Windows | 1.10.28 (8.1), 2.2.30 (8.3), 2.9.8 (8.4), 2.10.3 (8.5) |
-| macOS | 1.10.28 (8.1), 2.2.30 (8.3), 2.10.3 (8.5) |
+| macOS | 1.10.28 (8.1), 2.2.30 (8.3), 2.10.3 (8.4) |
 | Docker (Debian 12, PHP 8.2) | 2.2.30, 2.10.3 (`docker_e2e_vendor_composer`) |
 
 The capstones pin psr/log 3.0.2 (PHP ≥ 8.0) and, for the `v`-tagged cells,