diff --git a/Package.swift b/Package.swift
index 8f0a124..f692353 100644
--- a/Package.swift
+++ b/Package.swift
@@ -13,9 +13,9 @@ import PackageDescription
 
 
 #if swift(<6)
-let swiftConcurrency: SwiftSetting = .enableExperimentalFeature("SwiftConcurrency")
+let swiftConcurrency: SwiftSetting = .enableExperimentalFeature("StrictConcurrency")
 #else
-let swiftConcurrency: SwiftSetting = .enableUpcomingFeature("SwiftConcurrency")
+let swiftConcurrency: SwiftSetting = .enableUpcomingFeature("StrictConcurrency")
 #endif
 
 
@@ -34,7 +34,7 @@ let package = Package(
         .package(url: "https://github.com/StanfordSpezi/SpeziViews", from: "1.0.0"),
         .package(url: "https://github.com/apple/FHIRModels", .upToNextMinor(from: "0.5.0")),
         .package(url: "https://github.com/StanfordBDHG/ResearchKit", from: "3.0.1"),
-        .package(url: "https://github.com/StanfordBDHG/ResearchKitOnFHIR", from: "2.0.0")
+        .package(url: "https://github.com/StanfordBDHG/ResearchKitOnFHIR", from: "2.0.1")
     ] + swiftLintPackage(),
     targets: [
         .target(
@@ -89,7 +89,7 @@ func swiftLintPlugin() -> [Target.PluginUsage] {
 
 func swiftLintPackage() -> [PackageDescription.Package.Dependency] {
     if ProcessInfo.processInfo.environment["SPEZI_DEVELOPMENT_SWIFTLINT"] != nil {
-        [.package(url: "https://github.com/realm/SwiftLint.git", .upToNextMinor(from: "0.55.1"))]
+        [.package(url: "https://github.com/realm/SwiftLint.git", from: "0.55.1")]
     } else {
         []
     }
diff --git a/Sources/SpeziQuestionnaire/Identifier+Identifiable.swift b/Sources/SpeziQuestionnaire/Identifier+Identifiable.swift
index d8236e2..936f5c9 100644
--- a/Sources/SpeziQuestionnaire/Identifier+Identifiable.swift
+++ b/Sources/SpeziQuestionnaire/Identifier+Identifiable.swift
@@ -9,4 +9,8 @@
 import ModelsR4
 
 
-extension Identifier: Identifiable {}
+#if compiler(<6)
+extension ModelsR4.Identifier: Swift.Identifiable {}
+#else
+extension Identifier: @retroactive Identifiable {}
+#endif
diff --git a/Sources/SpeziQuestionnaire/QuestionnaireResult.swift b/Sources/SpeziQuestionnaire/QuestionnaireResult.swift
index 172ff6c..483cb46 100644
--- a/Sources/SpeziQuestionnaire/QuestionnaireResult.swift
+++ b/Sources/SpeziQuestionnaire/QuestionnaireResult.swift
@@ -18,3 +18,6 @@ public enum QuestionnaireResult {
     /// The questionnaire task failed due to an error.
     case failed
 }
+
+
+extension QuestionnaireResult: Hashable {}
diff --git a/Sources/SpeziQuestionnaire/QuestionnaireView.swift b/Sources/SpeziQuestionnaire/QuestionnaireView.swift
index 6dff988..6bd4ac2 100644
--- a/Sources/SpeziQuestionnaire/QuestionnaireView.swift
+++ b/Sources/SpeziQuestionnaire/QuestionnaireView.swift
@@ -40,7 +40,7 @@ public struct QuestionnaireView: View {
     private static let logger = Logger(subsystem: "edu.stanford.spezi.questionnaire", category: "QuestionnaireView")
 
     private let questionnaire: Questionnaire
-    private let questionnaireResult: (QuestionnaireResult) async -> Void
+    private let questionnaireResult: @MainActor (QuestionnaireResult) async -> Void
     private let completionStepMessage: String?
     private let cancelBehavior: CancelBehavior
     
diff --git a/Sources/SpeziTimedWalkTest/TimedWalkTest.swift b/Sources/SpeziTimedWalkTest/TimedWalkTest.swift
index 5e61a6d..18fe84e 100644
--- a/Sources/SpeziTimedWalkTest/TimedWalkTest.swift
+++ b/Sources/SpeziTimedWalkTest/TimedWalkTest.swift
@@ -10,7 +10,7 @@ import Foundation
 
 
 /// Defines the configuration of a timed walk test.
-public struct TimedWalkTest: Codable, Equatable, Hashable {
+public struct TimedWalkTest: Codable, Equatable, Hashable, Sendable {
     /// Default values.
     public enum Defaults {
         /// Default timed walk test duration.
diff --git a/Sources/SpeziTimedWalkTest/TimedWalkTestCompletedView.swift b/Sources/SpeziTimedWalkTest/TimedWalkTestCompletedView.swift
index ae263b3..a39ce52 100644
--- a/Sources/SpeziTimedWalkTest/TimedWalkTestCompletedView.swift
+++ b/Sources/SpeziTimedWalkTest/TimedWalkTestCompletedView.swift
@@ -39,7 +39,7 @@ struct TimedWalkTestCompletedView: View {
             Button("Restart", role: .destructive) {
                 dismiss()
             }
-            AsyncButton(action: completeAction) {
+            Button(action: completeAction) {
                 Text("Done")
                     .frame(maxWidth: .infinity, minHeight: 38)
             }
@@ -68,8 +68,9 @@ struct TimedWalkTestCompletedView: View {
             .bold()
             .padding()
     }
-    
-    private func completeAction() async {
+
+    @MainActor
+    private func completeAction() {
         walkTestViewModel.completeWalkTest()
     }
 }
diff --git a/Sources/SpeziTimedWalkTest/TimedWalkTestRunningView.swift b/Sources/SpeziTimedWalkTest/TimedWalkTestRunningView.swift
index 231197a..ec82016 100644
--- a/Sources/SpeziTimedWalkTest/TimedWalkTestRunningView.swift
+++ b/Sources/SpeziTimedWalkTest/TimedWalkTestRunningView.swift
@@ -69,7 +69,8 @@ struct TimedWalkTestRunningView: View {
             .modifier(TimedWalkTestCancelModifier())
     }
     
-    
+
+    @MainActor
     private func start() async {
         withAnimation {
             prepareCountDown = Date.now.addingTimeInterval(5)
diff --git a/Sources/SpeziTimedWalkTest/TimedWalkTestView.swift b/Sources/SpeziTimedWalkTest/TimedWalkTestView.swift
index 99bf99c..9799938 100644
--- a/Sources/SpeziTimedWalkTest/TimedWalkTestView.swift
+++ b/Sources/SpeziTimedWalkTest/TimedWalkTestView.swift
@@ -68,7 +68,8 @@ public struct TimedWalkTestView: View {
             .environment(walkTestViewModel)
     }
 
-    
+
+    @MainActor
     public init(
         timedWalkTest: TimedWalkTest = TimedWalkTest(),
         completion: @escaping (TimedWalkTestViewResult) -> Void
diff --git a/Sources/SpeziTimedWalkTest/TimedWalkTestViewModel.swift b/Sources/SpeziTimedWalkTest/TimedWalkTestViewModel.swift
index 72b4c39..f9b4379 100644
--- a/Sources/SpeziTimedWalkTest/TimedWalkTestViewModel.swift
+++ b/Sources/SpeziTimedWalkTest/TimedWalkTestViewModel.swift
@@ -11,8 +11,9 @@ import Foundation
 import SwiftUI
 
 
+@MainActor
 @Observable
-class TimedWalkTestViewModel {
+class TimedWalkTestViewModel: Sendable {
     let pedometer = CMPedometer()
     
     let timedWalkTest: TimedWalkTest