diff --git a/Sources/PackageLoading/TargetSourcesBuilder.swift b/Sources/PackageLoading/TargetSourcesBuilder.swift
index 2fff78a4d60..8c18eb83613 100644
--- a/Sources/PackageLoading/TargetSourcesBuilder.swift
+++ b/Sources/PackageLoading/TargetSourcesBuilder.swift
@@ -567,7 +567,7 @@ public struct FileRuleDescription: Sendable {
     /// A rule semantically describes a file/directory in a target.
     ///
     /// It is up to the build system to translate a rule into a build command.
-    public enum Rule: Equatable {
+    public enum Rule: Sendable, Equatable {
         /// The compile rule for `sources` in a package.
         case compile