diff --git a/Package.swift b/Package.swift
index ef516d2..bf68e88 100644
--- a/Package.swift
+++ b/Package.swift
@@ -27,7 +27,7 @@ let package = Package(
         ),
         .testTarget(
             name: "ClaudeUsageTests",
-            dependencies: ["ClaudeUsageCore"],
+            dependencies: ["ClaudeUsageCore", "ClaudeUsageApp"],
             path: "Tests/ClaudeUsageTests"
         ),
     ]
diff --git a/Sources/ClaudeUsageApp/StatusBarController.swift b/Sources/ClaudeUsageApp/StatusBarController.swift
index df26a1d..66a1e2b 100644
--- a/Sources/ClaudeUsageApp/StatusBarController.swift
+++ b/Sources/ClaudeUsageApp/StatusBarController.swift
@@ -68,6 +68,7 @@ final class StatusBarController: NSObject {
 
         NotificationCenter.default
             .publisher(for: UserDefaults.didChangeNotification)
+            .receiveOnMainQueue()
             .sink { [weak self] _ in
                 DispatchQueue.main.async { [weak self] in
                     self?.updateStatusItemLength()
@@ -102,3 +103,9 @@ final class StatusBarController: NSObject {
         popover.contentViewController?.view.window?.makeFirstResponder(nil)
     }
 }
+
+extension Publisher {
+    func receiveOnMainQueue() -> Publishers.ReceiveOn<Self, DispatchQueue> {
+        receive(on: DispatchQueue.main)
+    }
+}
diff --git a/Tests/ClaudeUsageTests/MainQueuePublisherTests.swift b/Tests/ClaudeUsageTests/MainQueuePublisherTests.swift
new file mode 100644
index 0000000..cdc1c4a
--- /dev/null
+++ b/Tests/ClaudeUsageTests/MainQueuePublisherTests.swift
@@ -0,0 +1,63 @@
+import Combine
+import Foundation
+import Testing
+@testable import ClaudeUsageApp
+
+@Suite("Main queue publishers")
+struct MainQueuePublisherTests {
+    @Test("receiveOnMainQueue delivers background notifications on main thread")
+    func receiveOnMainQueueDeliversOnMainThread() async throws {
+        let deliveredOnMainThread = ThreadFlag()
+        var cancellables = Set<AnyCancellable>()
+
+        NotificationCenter.default
+            .publisher(for: UserDefaults.didChangeNotification)
+            .receiveOnMainQueue()
+            .sink { _ in
+                deliveredOnMainThread.set(Thread.isMainThread)
+            }
+            .store(in: &cancellables)
+
+        await Task.detached {
+            NotificationCenter.default.post(name: UserDefaults.didChangeNotification, object: nil)
+        }.value
+
+        try await waitUntil(deliveredOnMainThread.hasValue)
+        #expect(deliveredOnMainThread.value == true)
+    }
+}
+
+private final class ThreadFlag: @unchecked Sendable {
+    private let lock = NSLock()
+    private var storedValue: Bool?
+
+    var value: Bool? {
+        lock.lock()
+        defer { lock.unlock() }
+        return storedValue
+    }
+
+    func set(_ value: Bool) {
+        lock.lock()
+        defer { lock.unlock() }
+        storedValue = value
+    }
+
+    func hasValue() -> Bool {
+        value != nil
+    }
+}
+
+private func waitUntil(
+    _ condition: @escaping @Sendable () -> Bool,
+    timeout: Duration = .seconds(1)
+) async throws {
+    let deadline = ContinuousClock.now + timeout
+    while !condition() {
+        if ContinuousClock.now >= deadline {
+            Issue.record("Timed out waiting for condition")
+            return
+        }
+        try await Task.sleep(for: .milliseconds(10))
+    }
+}