diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index cc262c5..4131f82 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -123,7 +123,11 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-latest, macos-latest, windows-latest]
+        # macOS is pinned, not -latest: the wheel's deployment target and
+        # the runner's Homebrew bottles must agree. See MACOSX_DEPLOYMENT_TARGET
+        # below. The test matrix above stays on macos-latest — it installs
+        # editable and never runs delocate, so it is unaffected.
+        os: [ubuntu-latest, macos-15, windows-latest]
     steps:
       - uses: actions/checkout@v7
 
@@ -159,9 +163,15 @@ jobs:
           # its default Windows repair command — once we override
           # CIBW_REPAIR_WHEEL_COMMAND_WINDOWS we have to install it.
           CIBW_BEFORE_BUILD_WINDOWS: pip install delvewheel
-          # macOS: Homebrew's bottled dylibs are built for the runner's
-          # OS (macos-latest = 15). Set the wheel's deployment target
-          # to match so delocate accepts them.
+          # macOS: Homebrew's bottled dylibs are built for the runner's OS,
+          # and delocate refuses to bundle dylibs whose min target is newer
+          # than the wheel's. So this value and the runner image are ONE
+          # decision: keep it equal to the pinned macos-15 in the matrix
+          # above. Do not switch that runner to macos-latest — GitHub rolled
+          # macos-latest to macOS 26 in July 2026, whose bottles target 26.0,
+          # which broke this job for six weeks (#18). Raising both together
+          # is a support-floor change: it drops every macOS user below the
+          # new value, so it is a release decision, not a CI tweak.
           MACOSX_DEPLOYMENT_TARGET: "15.0"
           CIBW_ENVIRONMENT_WINDOWS: >-
             CMAKE_TOOLCHAIN_FILE="$VCPKG_INSTALLATION_ROOT/scripts/buildsystems/vcpkg.cmake"
diff --git a/.github/workflows/publish.yml b/.github/workflows/publish.yml
index 0871226..7cb9603 100644
--- a/.github/workflows/publish.yml
+++ b/.github/workflows/publish.yml
@@ -54,11 +54,17 @@ jobs:
           # macOS users fall back to a source build via the published
           # sdist for now; we'll add the x86_64 wheel back via
           # universal2 (or a self-hosted runner) in a follow-up.
-          # Deployment target must match the runner: Homebrew's bottled
-          # protobuf/abseil dylibs are built for the runner's macOS
-          # version (macos-latest = 15), and delocate refuses to bundle
-          # dylibs whose min target is newer than the wheel's.
-          - os: macos-latest
+          # The runner image and macosx_deployment_target below are ONE
+          # decision, not two: Homebrew's bottled protobuf/abseil dylibs are
+          # built for the runner's macOS version, and delocate refuses to
+          # bundle dylibs whose min target is newer than the wheel's. So the
+          # runner is pinned rather than -latest. GitHub rolled macos-latest
+          # to macOS 26 in July 2026, whose bottles target 26.0, silently
+          # breaking the macOS wheel against the 15.0 target here (#18).
+          # Raising this pair sets the published wheel's macOS support floor
+          # — it drops every macOS user below the new value — so it is a
+          # release decision. Keep the two values equal.
+          - os: macos-15
             archs: "arm64"
             macosx_deployment_target: "15.0"
           - os: windows-latest