diff --git a/pack.inc.php b/pack.inc.php
index cbee470..e78d2d8 100644
--- a/pack.inc.php
+++ b/pack.inc.php
@@ -458,18 +458,20 @@ function _config_patch_bundle_fmt3(
       $chunk_entries = array_filter($header, fn($item) => $item[4] == $chunk_offset); 
 
       //chunk contains only one patch entry
-      $patched_chunk = lz4_compress($patch_payload, 9);
-      if(strlen($patched_chunk) > $max_chunk_size)
-        $max_chunk_size = strlen($patched_chunk);
+      $patch_payload_lz4 = lz4_compress($patch_payload, 9); 
+      $patched_chunk = pack("V", strlen($patch_payload_lz4));
+      $patched_chunk .= $patch_payload_lz4;
+      if(strlen($patch_payload) > $max_chunk_size)
+        $max_chunk_size = strlen($patch_payload);
 
       //TODO: make a better generic algorithm for patching the whole chunk
       //special case for single entry 
       if(count($chunk_entries) == 1 && $payloads_offset == 0)
       {
-        $lz4_chunk_size = unpack("V", substr($packed_data, $chunk_offset, 4))[1];
+        $lz4_chunk_size = unpack("V", substr($payloads_bundle, $chunk_offset, 4))[1];
 
         //we can just replace chunk in place if the size of a patched chunk is less or equal
-        if(strlen($patched_chunk) <= $lz4_chunk_size)
+        if(strlen($patch_payload_lz4) <= $lz4_chunk_size)
         {
           $payloads_bundle = substr_replace($payloads_bundle, $patched_chunk, $chunk_offset, strlen($patched_chunk));
           $header_entry[6] = strlen($patch_payload);