diff --git a/Sources/FrontEnd/TypedProgram.swift b/Sources/FrontEnd/TypedProgram.swift
index 28b0b023d..3e643d45d 100644
--- a/Sources/FrontEnd/TypedProgram.swift
+++ b/Sources/FrontEnd/TypedProgram.swift
@@ -129,7 +129,7 @@ public struct TypedProgram {
   }
 
   /// The type checking of a collection of source files.
-  private final class TypeCheckTask: Operation {
+  private final class TypeCheckTask: Operation, @unchecked Sendable {
 
     /// The sources to check.
     private let sources: [TranslationUnit.ID]