diff --git a/Sources/BuildSystemIntegration/BuildServerBuildSystem.swift b/Sources/BuildSystemIntegration/BuildServerBuildSystem.swift
index cd35fd81..ac9b9e4d 100644
--- a/Sources/BuildSystemIntegration/BuildServerBuildSystem.swift
+++ b/Sources/BuildSystemIntegration/BuildServerBuildSystem.swift
@@ -333,11 +333,6 @@ extension BuildServerBuildSystem: BuiltInBuildSystem {
   package func waitForUpBuildSystemUpdates(request: WaitForBuildSystemUpdatesRequest) async -> VoidResponse {
     return VoidResponse()
   }
-
-  package func addSourceFilesDidChangeCallback(_ callback: @escaping () async -> Void) {
-    // BuildServerBuildSystem does not support syntactic test discovery or background indexing.
-    // (https://github.com/swiftlang/sourcekit-lsp/issues/1173).
-  }
 }
 
 private func loadBuildServerConfig(path: AbsolutePath, fileSystem: FileSystem) throws -> BuildServerConfig {
diff --git a/Sources/BuildSystemIntegration/BuildSystemDelegate.swift b/Sources/BuildSystemIntegration/BuildSystemDelegate.swift
index b37778e5..fc947f33 100644
--- a/Sources/BuildSystemIntegration/BuildSystemDelegate.swift
+++ b/Sources/BuildSystemIntegration/BuildSystemDelegate.swift
@@ -32,4 +32,7 @@ package protocol BuildSystemManagerDelegate: AnyObject, Sendable {
 
   /// Log the given message to the client's index log.
   func logMessageToIndexLog(taskID: IndexTaskID, message: String)
+
+  /// Notify the delegate that the list of source files in the build system might have changed.
+  func sourceFilesDidChange() async
 }
diff --git a/Sources/BuildSystemIntegration/BuildSystemManager.swift b/Sources/BuildSystemIntegration/BuildSystemManager.swift
index f4516cf8..e0e2dadf 100644
--- a/Sources/BuildSystemIntegration/BuildSystemManager.swift
+++ b/Sources/BuildSystemIntegration/BuildSystemManager.swift
@@ -709,6 +709,7 @@ extension BuildSystemManager {
     // FIXME: (BSP Migration) Communicate that the build target has changed to the `BuildSystemManagerDelegate` and make
     // it responsible for figuring out which files are affected.
     await delegate?.fileBuildSettingsChanged(Set(watchedFiles.keys))
+    await self.delegate?.sourceFilesDidChange()
   }
 
   private func logMessage(notification: BuildServerProtocol.LogMessageNotification) async {
diff --git a/Sources/BuildSystemIntegration/BuiltInBuildSystem.swift b/Sources/BuildSystemIntegration/BuiltInBuildSystem.swift
index 41ff1c80..0d9fd420 100644
--- a/Sources/BuildSystemIntegration/BuiltInBuildSystem.swift
+++ b/Sources/BuildSystemIntegration/BuiltInBuildSystem.swift
@@ -104,9 +104,4 @@ package protocol BuiltInBuildSystem: AnyObject, Sendable {
 
   /// Wait until the build graph has been loaded.
   func waitForUpBuildSystemUpdates(request: WaitForBuildSystemUpdatesRequest) async -> VoidResponse
-
-  /// Adds a callback that should be called when the value returned by `sourceFiles()` changes.
-  ///
-  /// The callback might also be called without an actual change to `sourceFiles`.
-  func addSourceFilesDidChangeCallback(_ callback: @Sendable @escaping () async -> Void) async
 }
diff --git a/Sources/BuildSystemIntegration/CompilationDatabaseBuildSystem.swift b/Sources/BuildSystemIntegration/CompilationDatabaseBuildSystem.swift
index 28a9f227..2647332d 100644
--- a/Sources/BuildSystemIntegration/CompilationDatabaseBuildSystem.swift
+++ b/Sources/BuildSystemIntegration/CompilationDatabaseBuildSystem.swift
@@ -206,8 +206,4 @@ extension CompilationDatabaseBuildSystem: BuiltInBuildSystem {
       await testFilesDidChangeCallback()
     }
   }
-
-  package func addSourceFilesDidChangeCallback(_ callback: @escaping () async -> Void) async {
-    testFilesDidChangeCallbacks.append(callback)
-  }
 }
diff --git a/Sources/BuildSystemIntegration/SwiftPMBuildSystem.swift b/Sources/BuildSystemIntegration/SwiftPMBuildSystem.swift
index a42f0807..95af08e6 100644
--- a/Sources/BuildSystemIntegration/SwiftPMBuildSystem.swift
+++ b/Sources/BuildSystemIntegration/SwiftPMBuildSystem.swift
@@ -795,10 +795,6 @@ extension SwiftPMBuildSystem: BuildSystemIntegration.BuiltInBuildSystem {
     }
   }
 
-  package func addSourceFilesDidChangeCallback(_ callback: @Sendable @escaping () async -> Void) async {
-    testFilesDidChangeCallbacks.append(callback)
-  }
-
   /// Retrieve settings for a package manifest (Package.swift).
   private func settings(forPackageManifest path: AbsolutePath) throws -> SourceKitOptionsResponse? {
     let compilerArgs = workspace.interpreterFlags(for: path.parentDirectory) + [path.pathString]
diff --git a/Sources/BuildSystemIntegration/TestBuildSystem.swift b/Sources/BuildSystemIntegration/TestBuildSystem.swift
index f0baad43..d8f48d0a 100644
--- a/Sources/BuildSystemIntegration/TestBuildSystem.swift
+++ b/Sources/BuildSystemIntegration/TestBuildSystem.swift
@@ -77,6 +77,4 @@ package actor TestBuildSystem: BuiltInBuildSystem {
   package func topologicalSort(of targets: [BuildTargetIdentifier]) -> [BuildTargetIdentifier]? {
     return nil
   }
-
-  package func addSourceFilesDidChangeCallback(_ callback: @escaping () async -> Void) async {}
 }
diff --git a/Sources/SourceKitLSP/Workspace.swift b/Sources/SourceKitLSP/Workspace.swift
index fa1fc6f7..c58ec8c1 100644
--- a/Sources/SourceKitLSP/Workspace.swift
+++ b/Sources/SourceKitLSP/Workspace.swift
@@ -130,15 +130,6 @@ package final class Workspace: Sendable, BuildSystemManagerDelegate {
     await indexDelegate?.addMainFileChangedCallback { [weak self] in
       await self?.buildSystemManager.mainFilesChanged()
     }
-    await buildSystemManager.buildSystem?.underlyingBuildSystem.addSourceFilesDidChangeCallback { [weak self] in
-      guard let self else {
-        return
-      }
-      guard let testFiles = await orLog("Getting test files", { try await self.buildSystemManager.testFiles() }) else {
-        return
-      }
-      await self.syntacticTestIndex.listOfTestFilesDidChange(testFiles)
-    }
     // Trigger an initial population of `syntacticTestIndex`.
     if let testFiles = await orLog("Getting initial test files", { try await self.buildSystemManager.testFiles() }) {
       await syntacticTestIndex.listOfTestFilesDidChange(testFiles)
@@ -328,6 +319,11 @@ package final class Workspace: Sendable, BuildSystemManagerDelegate {
   package func logMessageToIndexLog(taskID: IndexTaskID, message: String) {
     self.logMessageToIndexLogCallback(taskID, message)
   }
+
+  package func sourceFilesDidChange() async {
+    let testFiles = await orLog("Getting test files") { try await buildSystemManager.testFiles() } ?? []
+    await syntacticTestIndex.listOfTestFilesDidChange(testFiles)
+  }
 }
 
 /// Wrapper around a workspace that isn't being retained.
diff --git a/Tests/BuildSystemIntegrationTests/BuildSystemManagerTests.swift b/Tests/BuildSystemIntegrationTests/BuildSystemManagerTests.swift
index b11a4858..3728ec59 100644
--- a/Tests/BuildSystemIntegrationTests/BuildSystemManagerTests.swift
+++ b/Tests/BuildSystemIntegrationTests/BuildSystemManagerTests.swift
@@ -406,4 +406,6 @@ private actor BSMDelegate: BuildSystemManagerDelegate {
   func buildTargetsChanged(_ changes: [BuildTargetEvent]?) async {}
 
   nonisolated func logMessageToIndexLog(taskID: BuildSystemIntegration.IndexTaskID, message: String) {}
+
+  func sourceFilesDidChange() async {}
 }