diff --git a/.github/workflows/check.yaml b/.github/workflows/check.yaml
index b719af1a..7755b474 100644
--- a/.github/workflows/check.yaml
+++ b/.github/workflows/check.yaml
@@ -1,7 +1,5 @@
 name: Check
 
-# TODO fail-fast or whatever it's called
-
 on:
   workflow_dispatch:
   pull_request:
@@ -14,7 +12,11 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        xcode-version: [15.3, 16-beta]
+        tooling:
+          - xcode-version: 15.3
+            swift-version: 5
+          - xcode-version: 16-beta
+            swift-version: 6
     steps:
       - uses: actions/checkout@v4
       - uses: maxim-lobanov/setup-xcode@v1
@@ -27,8 +29,8 @@ jobs:
       - run: script/lint/check
 
       # https://forums.swift.org/t/warnings-as-errors-for-libraries-frameworks/58393/2
-      - run: swift build -Xswiftc -warnings-as-errors
-      - run: swift test
+      - run: swift build -Xswiftc -warnings-as-errors -Xswiftc -swift-version -Xswiftc ${{ matrix.tooling.swift-version }}
+      - run: swift test -Xswiftc -warnings-as-errors -Xswiftc -swift-version -Xswiftc ${{ matrix.tooling.swift-version }}
 
   check-on-platforms:
     runs-on: macos-latest
@@ -36,14 +38,18 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        xcode-version: [15.3, 16-beta]
+        tooling:
+          - xcode-version: 15.3
+            swift-version: 5
+          - xcode-version: 16-beta
+            swift-version: 6
         platform: [macOS, iOS, tvOS]
 
     steps:
       - uses: actions/checkout@v4
       - uses: maxim-lobanov/setup-xcode@v1
         with:
-          xcode-version: ${{ matrix.xcode-version }}
+          xcode-version: ${{ matrix.tooling.xcode-version }}
 
       # TODO OS version, and ambiguity in platforms, and no match
       - run: xcodebuild -scheme AblyChat -destination "platform=${{ matrix.platform }}"