diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 2d2d1f2be5..c27816dd89 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -10,33 +10,33 @@ on:
   workflow_dispatch:
 
 jobs:
-  macos_tests:
-    runs-on: macos-12
+  macos:
+    runs-on: macos-14
     strategy:
       matrix:
         xcode:
-          - "14.2" # Swift 5.7.2
-        command:
-          - test
-          # - benchmarks
+          - '16.0'
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Select Xcode ${{ matrix.xcode }}
         run: sudo xcode-select -s /Applications/Xcode_${{ matrix.xcode }}.app
       - name: System
         run: system_profiler SPHardwareDataType
-      - name: Run ${{ matrix.command }}
-        run: make ${{ matrix.command }}
+      - name: Build
+        run: swift build
+      - name: Run tests
+        run: swift test
 
-  ubuntu_tests:
+  linux:
     strategy:
       matrix:
-        os: [ubuntu-20.04]
-
+        os: [ubuntu-latest]
+        swift:
+          - '6.0'
     runs-on: ${{ matrix.os }}
-
+    container: swift:${{ matrix.swift }}
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Build
         run: swift build
       - name: Run tests
diff --git a/Sources/swift-parsing-benchmark/JSON.swift b/Sources/swift-parsing-benchmark/JSON.swift
index 18d4921d67..8227de22cb 100644
--- a/Sources/swift-parsing-benchmark/JSON.swift
+++ b/Sources/swift-parsing-benchmark/JSON.swift
@@ -70,7 +70,8 @@ let jsonSuite = BenchmarkSuite(name: "JSON") { suite in
     struct JSONObject: ParserPrinter {
       var body: some ParserPrinter<Substring.UTF8View, [String: JSONValue.Output]> {
         "{".utf8
-        Many(into: [String: JSONValue.Output]()) { object, pair in
+        Many(into: [String: JSONValue.Output]()) {
+          (object: inout [String: JSONValue.Output], pair: (String, JSONValue.Output)) in
           let (name, value) = pair
           object[name] = value
         } decumulator: { object in
diff --git a/Tests/ParsingTests/FromSubstringTests.swift b/Tests/ParsingTests/FromSubstringTests.swift
index a1bd95552e..2e4f8cac19 100644
--- a/Tests/ParsingTests/FromSubstringTests.swift
+++ b/Tests/ParsingTests/FromSubstringTests.swift
@@ -1,6 +1,7 @@
 import Parsing
 import XCTest
 
+@available(*, deprecated)
 final class FromSubstringTests: XCTestCase {
   func testUTF8View() {
     let p = Parse(input: Substring.UTF8View.self) {
diff --git a/Tests/ParsingTests/OneOfTests.swift b/Tests/ParsingTests/OneOfTests.swift
index b0d829a53b..9c77ec68d7 100644
--- a/Tests/ParsingTests/OneOfTests.swift
+++ b/Tests/ParsingTests/OneOfTests.swift
@@ -271,7 +271,8 @@ final class OneOfTests: XCTestCase {
       struct JSONObject: ParserPrinter {
         var body: some ParserPrinter<Substring.UTF8View, [String: JSONValue.Output]> {
           "{".utf8
-          Many(into: [String: JSONValue.Output]()) { object, pair in
+          Many(into: [String: JSONValue.Output]()) {
+            (object: inout [String: JSONValue.Output], pair: (String, JSONValue.Output)) in
             let (name, value) = pair
             object[name] = value
           } decumulator: { object in