diff --git a/pkl-core/src/main/java/org/pkl/core/packages/PackageResolvers.java b/pkl-core/src/main/java/org/pkl/core/packages/PackageResolvers.java
index a0fde8e6..1c79f2a2 100644
--- a/pkl-core/src/main/java/org/pkl/core/packages/PackageResolvers.java
+++ b/pkl-core/src/main/java/org/pkl/core/packages/PackageResolvers.java
@@ -554,7 +554,7 @@ class PackageResolvers {
     private FileSystem getZipFileSystem(PackageAssetUri uri, @Nullable Checksums checksums)
         throws IOException, SecurityManagerException {
       var packageUri = uri.getPackageUri();
-      synchronized (fileSystems) {
+      synchronized (lock) {
         var fs = fileSystems.get(packageUri);
         if (fs == null) {
           var metadata = getDependencyMetadata(packageUri, checksums);