diff --git a/src/main/java/com/dostalgia/GameService.java b/src/main/java/com/dostalgia/GameService.java
index 5a31600..0c34d1b 100644
--- a/src/main/java/com/dostalgia/GameService.java
+++ b/src/main/java/com/dostalgia/GameService.java
@@ -171,7 +171,7 @@ public class GameService {
         byte[] newJsdosJson = buildJsdosJsonBytes(executable);
 
         // Patch the ZIP: read old, write new with modified config entries
-        Path tmpPath = bundlePath.resolveSibling(bundleFile + ".tmp");
+        Path tmpPath = bundlePath.resolveSibling(bundlePath.getFileName() + ".tmp");
         try (var zis = new java.util.zip.ZipInputStream(Files.newInputStream(bundlePath));
              var zos = new java.util.zip.ZipOutputStream(Files.newOutputStream(tmpPath))) {