diff --git a/Sources/DefaultAppsCore/Homebrew.swift b/Sources/DefaultAppsCore/Homebrew.swift
index 500ff8b..b196299 100644
--- a/Sources/DefaultAppsCore/Homebrew.swift
+++ b/Sources/DefaultAppsCore/Homebrew.swift
@@ -3,11 +3,20 @@ import Foundation
 public enum Homebrew {
     public static let standardPrefixes = [URL(filePath: "/opt/homebrew"), URL(filePath: "/usr/local")]
 
-    /// True when the app came in through `brew install --cask`, so
-    /// `brew upgrade` already covers updates.
-    public static func managesApp(prefixes: [URL] = standardPrefixes) -> Bool {
-        prefixes.contains {
-            FileManager.default.fileExists(atPath: $0.appending(path: "Caskroom/macosdefaultapps").path)
+    /// True when `bundle` is the app `brew install --cask` put in place, so
+    /// `brew upgrade` already covers updates. The cask existing is not enough:
+    /// a dev build or a zip copy can run next to it.
+    public static func managesApp(at bundle: URL = Bundle.main.bundleURL, prefixes: [URL] = standardPrefixes)
+        -> Bool
+    {
+        let running = bundle.resolvingSymlinksInPath()
+        let fileManager = FileManager.default
+        return prefixes.contains { prefix in
+            let cask = prefix.appending(path: "Caskroom/macosdefaultapps")
+            let versions = (try? fileManager.contentsOfDirectory(atPath: cask.path)) ?? []
+            return versions.contains { version in
+                cask.appending(path: "\(version)/macOSDefaultApps.app").resolvingSymlinksInPath() == running
+            }
         }
     }
 }
diff --git a/Tests/DefaultAppsCoreTests/HomebrewTests.swift b/Tests/DefaultAppsCoreTests/HomebrewTests.swift
index bf32c3f..64935cd 100644
--- a/Tests/DefaultAppsCoreTests/HomebrewTests.swift
+++ b/Tests/DefaultAppsCoreTests/HomebrewTests.swift
@@ -7,20 +7,34 @@ struct HomebrewTests {
     let root = FileManager.default.temporaryDirectory
         .appending(path: "mda-homebrew-tests-\(UUID().uuidString)")
 
-    @Test("an installed cask means brew owns updates")
-    func caskInstalled() throws {
-        try FileManager.default.createDirectory(
-            at: root.appending(path: "Caskroom/macosdefaultapps/0.7.1"), withIntermediateDirectories: true)
+    var installed: URL { root.appending(path: "Applications/macOSDefaultApps.app") }
 
-        #expect(Homebrew.managesApp(prefixes: [root.appending(path: "missing"), root]))
+    /// What `brew install --cask` leaves behind: a versioned symlink to the app it moved.
+    func installCask(version: String = "0.7.1") throws {
+        let versionDir = root.appending(path: "brew/Caskroom/macosdefaultapps/\(version)")
+        try FileManager.default.createDirectory(at: versionDir, withIntermediateDirectories: true)
+        try FileManager.default.createDirectory(at: installed, withIntermediateDirectories: true)
+        try FileManager.default.createSymbolicLink(
+            at: versionDir.appending(path: "macOSDefaultApps.app"), withDestinationURL: installed)
     }
 
-    @Test("no cask, or no homebrew at all, means nobody updates it for us")
-    func noCask() throws {
-        try FileManager.default.createDirectory(
-            at: root.appending(path: "Caskroom/something-else"), withIntermediateDirectories: true)
+    @Test("the running app is the one the cask installed")
+    func runningTheCask() throws {
+        try installCask()
 
-        #expect(!Homebrew.managesApp(prefixes: [root]))
-        #expect(!Homebrew.managesApp(prefixes: [root.appending(path: "missing")]))
+        #expect(Homebrew.managesApp(at: installed, prefixes: [root.appending(path: "missing"), root.appending(path: "brew")]))
+    }
+
+    @Test("a cask is installed, but this copy came from somewhere else")
+    func runningAnotherCopy() throws {
+        try installCask()
+
+        #expect(!Homebrew.managesApp(at: root.appending(path: "Downloads/macOSDefaultApps.app"), prefixes: [root.appending(path: "brew")]))
+        #expect(!Homebrew.managesApp(at: root.appending(path: ".build/debug"), prefixes: [root.appending(path: "brew")]))
+    }
+
+    @Test("no homebrew at all means nobody updates it for us")
+    func noHomebrew() {
+        #expect(!Homebrew.managesApp(at: installed, prefixes: [root.appending(path: "missing")]))
     }
 }