diff --git a/tools/isobuild/package-source.js b/tools/isobuild/package-source.js
index 2ba1ac25e3..c3c0bc9de8 100644
--- a/tools/isobuild/package-source.js
+++ b/tools/isobuild/package-source.js
@@ -225,7 +225,7 @@ class SymlinkLoopChecker {
 
     if (files.lstat(absPath).isSymbolicLink()) {
       const result = files.realpath(absPath);
-      this._cache.set(relPath, result);
+      this._cache.set(relDir, result);
 
       return result;
   }