diff --git a/app/zip.js b/app/zip.js
index 6cc57b74..1363da82 100644
--- a/app/zip.js
+++ b/app/zip.js
@@ -50,7 +50,7 @@ class File {
     v.setUint32(0, 0x08074b50, true); // sig
     v.setUint32(4, this.crc, true); // crc32
     v.setUint32(8, this.size, true); // compressed size
-    v.setUint16(12, this.size, true); // uncompressed size
+    v.setUint32(12, this.size, true); // uncompressed size
     return new Uint8Array(dd);
   }
 
@@ -60,7 +60,7 @@ class File {
     v.setUint32(0, 0x02014b50, true); // sig
     v.setUint16(4, 20, true); // version made
     v.setUint16(6, 20, true); // version required
-    v.setUint16(8, 0, true); // bit flags
+    v.setUint16(8, 8, true); // bit flags (8 = use data descriptor)
     v.setUint16(10, 0, true); // compression
     v.setUint16(12, this.dateTime.time, true); // modified time
     v.setUint16(14, this.dateTime.date, true); // modified date