diff --git a/Sources/swift-parsing-benchmark/JSON.swift b/Sources/swift-parsing-benchmark/JSON.swift
index 18d4921d67..022e2e5b1d 100644
--- a/Sources/swift-parsing-benchmark/JSON.swift
+++ b/Sources/swift-parsing-benchmark/JSON.swift
@@ -70,7 +70,10 @@ 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/OneOfTests.swift b/Tests/ParsingTests/OneOfTests.swift
index b0d829a53b..86a0bb4e5f 100644
--- a/Tests/ParsingTests/OneOfTests.swift
+++ b/Tests/ParsingTests/OneOfTests.swift
@@ -271,7 +271,10 @@ 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