diff --git a/Source/SwiftLintCore/Extensions/SwiftLintFile+Cache.swift b/Source/SwiftLintCore/Extensions/SwiftLintFile+Cache.swift
index 66a535b6c..c48b0a417 100644
--- a/Source/SwiftLintCore/Extensions/SwiftLintFile+Cache.swift
+++ b/Source/SwiftLintCore/Extensions/SwiftLintFile+Cache.swift
@@ -55,7 +55,7 @@ private let swiftSyntaxTokensCache = Cache { file -> [SwiftLintSyntaxToken]? in
 package typealias AssertHandler = () -> Void
 // Re-enable once all parser diagnostics in tests have been addressed.
 // https://github.com/realm/SwiftLint/issues/3348
-package nonisolated(unsafe) var parserDiagnosticsDisabledForTests = false
+@TaskLocal package var parserDiagnosticsDisabledForTests = false
 
 private let assertHandlerCache = Cache { (_: SwiftLintFile) -> AssertHandler? in nil }
 
@@ -124,9 +124,9 @@ extension SwiftLintFile {
         }
     }
 
-    public var parserDiagnostics: [String]? {
+    public var parserDiagnostics: [String] {
         if parserDiagnosticsDisabledForTests {
-            return nil
+            return []
         }
 
         return ParseDiagnosticsGenerator.diagnostics(for: syntaxTree)
diff --git a/Source/SwiftLintFramework/Models/Linter.swift b/Source/SwiftLintFramework/Models/Linter.swift
index f0a3c12fe..1af72e043 100644
--- a/Source/SwiftLintFramework/Models/Linter.swift
+++ b/Source/SwiftLintFramework/Models/Linter.swift
@@ -408,11 +408,11 @@ public struct CollectedLinter {
             return [:]
         }
 
-        if let parserDiagnostics = file.parserDiagnostics, parserDiagnostics.isNotEmpty {
+        if file.parserDiagnostics.isNotEmpty {
             queuedPrintError(
                 "warning: Skipping correcting file because it produced Swift parser errors: \(file.path ?? "<nopath>")"
             )
-            queuedPrintError(toJSON(["diagnostics": parserDiagnostics]))
+            queuedPrintError(toJSON(["diagnostics": file.parserDiagnostics]))
             return [:]
         }
 
diff --git a/Tests/FrameworkTests/ParserDiagnosticsTests.swift b/Tests/FrameworkTests/ParserDiagnosticsTests.swift
index 8d1d4bec0..fad92d20d 100644
--- a/Tests/FrameworkTests/ParserDiagnosticsTests.swift
+++ b/Tests/FrameworkTests/ParserDiagnosticsTests.swift
@@ -5,8 +5,9 @@ import XCTest
 
 final class ParserDiagnosticsTests: SwiftLintTestCase {
     func testFileWithParserErrorDiagnostics() {
-        parserDiagnosticsDisabledForTests = false
-        XCTAssertNotNil(SwiftLintFile(contents: "importz Foundation").parserDiagnostics)
+        $parserDiagnosticsDisabledForTests.withValue(false) {
+            XCTAssertNotNil(SwiftLintFile(contents: "importz Foundation").parserDiagnostics)
+        }
     }
 
     func testFileWithParserErrorDiagnosticsDoesntAutocorrect() throws {
@@ -24,7 +25,6 @@ final class ParserDiagnosticsTests: SwiftLintTestCase {
     }
 
     func testFileWithParserWarningDiagnostics() throws {
-        parserDiagnosticsDisabledForTests = false
         // extraneous duplicate parameter name; 'bar' already has an argument label
         let original = """
         func foo(bar bar: String) ->   Int { 0 }
@@ -34,7 +34,9 @@ final class ParserDiagnosticsTests: SwiftLintTestCase {
         func foo(bar bar: String) -> Int { 0 }
         """
 
-        XCTAssertEqual(SwiftLintFile(contents: original).parserDiagnostics, [])
+        $parserDiagnosticsDisabledForTests.withValue(false) {
+            XCTAssertEqual(SwiftLintFile(contents: original).parserDiagnostics, [])
+        }
 
         let ruleDescription = ReturnArrowWhitespaceRule.description
             .with(corrections: [Example(original): Example(corrected)])
@@ -45,7 +47,8 @@ final class ParserDiagnosticsTests: SwiftLintTestCase {
     }
 
     func testFileWithoutParserDiagnostics() {
-        parserDiagnosticsDisabledForTests = false
-        XCTAssertEqual(SwiftLintFile(contents: "import Foundation").parserDiagnostics, [])
+        $parserDiagnosticsDisabledForTests.withValue(false) {
+            XCTAssertEqual(SwiftLintFile(contents: "import Foundation").parserDiagnostics, [])
+        }
     }
 }
diff --git a/Tests/TestHelpers/TestHelpers.swift b/Tests/TestHelpers/TestHelpers.swift
index 10cdc8b23..d532dc777 100644
--- a/Tests/TestHelpers/TestHelpers.swift
+++ b/Tests/TestHelpers/TestHelpers.swift
@@ -439,23 +439,23 @@ public extension XCTestCase {
                            parserDiagnosticsDisabledForTests: Bool = true) {
         let ruleDescription = ruleDescription.focused()
 
-        SwiftLintCore.parserDiagnosticsDisabledForTests = parserDiagnosticsDisabledForTests
+        SwiftLintCore.$parserDiagnosticsDisabledForTests.withValue(parserDiagnosticsDisabledForTests) {
+            // corrections
+            ruleDescription.corrections.forEach {
+                testCorrection($0, configuration: config, testMultiByteOffsets: testMultiByteOffsets)
+            }
+            // make sure strings that don't trigger aren't corrected
+            ruleDescription.nonTriggeringExamples.forEach {
+                testCorrection(($0, $0), configuration: config, testMultiByteOffsets: testMultiByteOffsets)
+            }
 
-        // corrections
-        ruleDescription.corrections.forEach {
-            testCorrection($0, configuration: config, testMultiByteOffsets: testMultiByteOffsets)
-        }
-        // make sure strings that don't trigger aren't corrected
-        ruleDescription.nonTriggeringExamples.forEach {
-            testCorrection(($0, $0), configuration: config, testMultiByteOffsets: testMultiByteOffsets)
-        }
-
-        // "disable" commands do not correct
-        ruleDescription.corrections.forEach { before, _ in
-            for command in disableCommands {
-                let beforeDisabled = command + before.code
-                let expectedCleaned = before.with(code: cleanedContentsAndMarkerOffsets(from: beforeDisabled).0)
-                config.assertCorrection(expectedCleaned, expected: expectedCleaned)
+            // "disable" commands do not correct
+            ruleDescription.corrections.forEach { before, _ in
+                for command in disableCommands {
+                    let beforeDisabled = command + before.code
+                    let expectedCleaned = before.with(code: cleanedContentsAndMarkerOffsets(from: beforeDisabled).0)
+                    config.assertCorrection(expectedCleaned, expected: expectedCleaned)
+                }
             }
         }
     }