# UNDF: UNDF-2026-000000359
--- a/src/install/yarn.zig
+++ b/src/install/yarn.zig
@@ -773,20 +773,18 @@ fn populatePackageVersionMap(
                 var found_existing = false;
                 var found_new = false;
+                var found_package_id: Install.PackageID = 0;
                 for (list.items) |item| {
                     if (strings.eql(item.version, existing.version)) found_existing = true;
-                    if (strings.eql(item.version, version)) found_new = true;
+                    if (strings.eql(item.version, version)) {
+                        found_new = true;
+                        found_package_id = item.package_id;  // capture in first pass
+                    }
                 }

                 if (!found_existing) {
                     try list.append(.{
                         .yarn_idx = existing.yarn_idx,
                         .version = existing.version,
                         .package_id = existing.package_id,
                     });
                 }

                 if (!found_new) {
                     const package_id = next_package_id;
                     next_package_id += 1;
                     try list.append(.{
                         .yarn_idx = yarn_idx,
                         .version = version,
                         .package_id = package_id,
                     });
                     yarn_entry_to_package_id[yarn_idx] = package_id;
                 } else {
-                    for (list.items) |item| {   // O(M) second scan — eliminated
-                        if (strings.eql(item.version, version)) {
-                            yarn_entry_to_package_id[yarn_idx] = item.package_id;
-                            break;
-                        }
-                    }
+                    yarn_entry_to_package_id[yarn_idx] = found_package_id;
                 }