diff --git a/lib/std/Build/Cache.zig b/lib/std/Build/Cache.zig
index b3283856d9e64339cbaf153601aa80a0265bcefb..54f0b8baad329214e94a37d56173f04d04c4d082 100644
--- a/lib/std/Build/Cache.zig
+++ b/lib/std/Build/Cache.zig
@@ -1007,6 +1007,8 @@ pub const Manifest = struct {
         keep = try addPrefixedPathPost(self, prefixed_path);
     }
 
+    /// Low level function. `prefixed_path` references cloned memory. Returns
+    /// whether or not `prefixed_path.sub_path` should be kept.
     pub fn addPrefixedPathPost(man: *Manifest, prefixed_path: PrefixedPath) !bool {
         assert(man.manifest_file != null);
         const gpa = man.cache.gpa;
diff --git a/lib/std/zig.zig b/lib/std/zig.zig
index 6efe0cc7431e367f19add7b142db99641e6728b7..657b05638e03147e5d54d51b3768b97004333276 100644
--- a/lib/std/zig.zig
+++ b/lib/std/zig.zig
@@ -1754,8 +1754,10 @@ pub fn buildExeSubprocess(gpa: Allocator, io: Io, options: BuildExeSubprocessOpt
                 var it = mem.splitScalar(u8, body, 0);
                 while (it.next()) |prefixed_path| {
                     const prefix: Server.Message.PathPrefix = @enumFromInt(prefixed_path[0] - 1);
-                    const sub_path = prefixed_path[1..];
-                    _ = man.addPrefixedPathPost(.{
+                    const sub_path = try gpa.dupe(u8, prefixed_path[1..]);
+                    var keep = false;
+                    defer if (!keep) gpa.free(sub_path);
+                    keep = man.addPrefixedPathPost(.{
                         .prefix = @intFromEnum(prefix),
                         .sub_path = sub_path,
                     }) catch |err| switch (err) {