diff --git a/apkverify/src/ziputil.rs b/apkverify/src/ziputil.rs
index 28ecf87..dbf5131 100644
--- a/apkverify/src/ziputil.rs
+++ b/apkverify/src/ziputil.rs
@@ -17,7 +17,7 @@
 //! Utilities for zip handling
 
 use anyhow::{bail, Result};
-use bytes::Buf;
+use bytes::{Buf, BufMut};
 use std::io::{Read, Seek, SeekFrom};
 use zip::ZipArchive;
 
@@ -69,3 +69,12 @@
     }
     Ok((&buf[EOCD_CENTRAL_DIRECTORY_OFFSET_FIELD_OFFSET..]).get_u32_le())
 }
+
+/// Update EOCD's central_directory_offset field.
+pub fn set_central_directory_offset(buf: &mut [u8], value: u32) -> Result<()> {
+    if buf.len() < EOCD_MIN_SIZE {
+        bail!("Invalid EOCD size: {}", buf.len());
+    }
+    (&mut buf[EOCD_CENTRAL_DIRECTORY_OFFSET_FIELD_OFFSET..]).put_u32_le(value);
+    Ok(())
+}