diff --git a/src/main/java/com/dostalgia/UploadResource.java b/src/main/java/com/dostalgia/UploadResource.java
index 73523d4..ef7a8b1 100644
--- a/src/main/java/com/dostalgia/UploadResource.java
+++ b/src/main/java/com/dostalgia/UploadResource.java
@@ -296,47 +296,46 @@ public class UploadResource {
 
         // ZIP it up directly from extractDir (no temp copy)
         try (var zos = new java.util.zip.ZipOutputStream(Files.newOutputStream(bundlePath))) {
-            var addedDirs = new java.util.HashSet<String>();
 
-            // Helper: write a directory entry and all its ancestors if not yet added
-            // (Emscripten FS requires every directory in the chain as explicit entries)
-            java.util.function.Consumer<String> ensureDir = entryName -> {
-                int idx = entryName.lastIndexOf('/');
-                while (idx >= 0) {
-                    String parent = entryName.substring(0, idx + 1);
-                    if (addedDirs.add(parent)) {
+            // ── Phase 1: Collect all directory paths from the file tree ──
+            // js-dos C code (jsdos-libzip.c) iterates ZIP entries linearly and
+            // calls mkdir() on each directory entry. All parents must come
+            // before their children or mkdir() fails with exit(1).
+            var allDirs = new java.util.TreeSet<String>();
+            try (var walk = Files.walk(extractDir)) {
+                walk.filter(Files::isRegularFile).forEach(f -> {
+                    String entryName = extractDir.relativize(f).toString().replace('\\', '/');
+                    int idx = entryName.lastIndexOf('/');
+                    while (idx >= 0) {
+                        allDirs.add(entryName.substring(0, idx + 1));
+                        idx = entryName.lastIndexOf('/', idx - 1);
+                    }
+                });
+            }
+
+            // ── Phase 2: Write ALL directory entries first (sorted → shallowest first) ──
+            for (String dir : allDirs) {
+                zos.putNextEntry(new java.util.zip.ZipEntry(dir));
+                zos.closeEntry();
+            }
+
+            // ── Phase 3: .jsdos config files (must come before game files) ──
+            try (var walk = Files.walk(jsdos)) {
+                walk.filter(Files::isRegularFile)
+                    .sorted()
+                    .forEach(f -> {
                         try {
-                            zos.putNextEntry(new java.util.zip.ZipEntry(parent));
+                            String entryName = extractDir.relativize(f).toString().replace('\\', '/');
+                            zos.putNextEntry(new java.util.zip.ZipEntry(entryName));
+                            Files.copy(f, zos);
                             zos.closeEntry();
                         } catch (IOException e) {
                             throw new UncheckedIOException(e);
                         }
-                    }
-                    idx = entryName.lastIndexOf('/', idx - 1);
-                }
-            };
-
-            // Helper: write a single file entry with its directory chain
-            java.util.function.Consumer<Path> writeFile = f -> {
-                try {
-                    String entryName = extractDir.relativize(f).toString().replace('\\', '/');
-                    ensureDir.accept(entryName);
-                    zos.putNextEntry(new java.util.zip.ZipEntry(entryName));
-                    Files.copy(f, zos);
-                    zos.closeEntry();
-                } catch (IOException e) {
-                    throw new UncheckedIOException(e);
-                }
-            };
-
-            // ── First pass: .jsdos config files (must come first in ZIP) ──
-            try (var walk = Files.walk(jsdos)) {
-                walk.filter(Files::isRegularFile)
-                    .sorted() // deterministic order
-                    .forEach(writeFile);
+                    });
             }
 
-            // ── Second pass: all other game files ──
+            // ── Phase 4: All other game files ──
             try (var walk = Files.walk(extractDir)) {
                 walk.filter(Files::isRegularFile)
                     .filter(f -> !f.startsWith(jsdos))
@@ -345,8 +344,17 @@ public class UploadResource {
                         int dot = n.lastIndexOf('.');
                         return dot < 0 || !SKIP_EXT.contains(n.substring(dot));
                     })
-                    .sorted() // deterministic order
-                    .forEach(writeFile);
+                    .sorted()
+                    .forEach(f -> {
+                        try {
+                            String entryName = extractDir.relativize(f).toString().replace('\\', '/');
+                            zos.putNextEntry(new java.util.zip.ZipEntry(entryName));
+                            Files.copy(f, zos);
+                            zos.closeEntry();
+                        } catch (IOException e) {
+                            throw new UncheckedIOException(e);
+                        }
+                    });
             }
         }