diff --git a/.github/workflows/pull_request.yml b/.github/workflows/pull_request.yml
index d6c6642..d7e87ad 100644
--- a/.github/workflows/pull_request.yml
+++ b/.github/workflows/pull_request.yml
@@ -29,7 +29,7 @@ jobs:
     uses: swiftlang/github-workflows/.github/workflows/swift_package_test.yml@0.0.14
     with:
       enable_macos_checks: true
-      macos_xcode_versions: "[\"swift_6.2\", \"swift_6.3\"]"
+      macos_xcode_versions: '["swift_6.2", "swift_6.3", "swift_6.4"]'
       linux_swift_versions: "[\"6.2\", \"nightly-main\", \"nightly-6.3\"]"
       linux_build_command: swift test --disable-experimental-prebuilts  # prebuilt swift-syntax not building
       enable_windows_checks: false