diff --git a/dexlib2/src/main/java/org/jf/dexlib2/dexbacked/raw/HeaderItem.java b/dexlib2/src/main/java/org/jf/dexlib2/dexbacked/raw/HeaderItem.java
index ca55d67c..3499eadc 100644
--- a/dexlib2/src/main/java/org/jf/dexlib2/dexbacked/raw/HeaderItem.java
+++ b/dexlib2/src/main/java/org/jf/dexlib2/dexbacked/raw/HeaderItem.java
@@ -51,9 +51,15 @@ public class HeaderItem {
 
     public static final int CHECKSUM_OFFSET = 8;
 
+    // this is the start of the checksumed data
+    public static final int CHECKSUM_DATA_START_OFFSET = 12;
     public static final int SIGNATURE_OFFSET = 12;
     public static final int SIGNATURE_SIZE = 20;
 
+    // this is the start of the sha-1 hashed data
+    public static final int SIGNATURE_DATA_START_OFFSET = 32;
+    public static final int FILE_SIZE_OFFSET = 32;
+
     public static final int HEADER_SIZE_OFFSET = 36;
 
     public static final int ENDIAN_TAG_OFFSET = 40;
diff --git a/dexlib2/src/main/java/org/jf/dexlib2/writer/DexWriter.java b/dexlib2/src/main/java/org/jf/dexlib2/writer/DexWriter.java
index 1886db0c..fef28015 100644
--- a/dexlib2/src/main/java/org/jf/dexlib2/writer/DexWriter.java
+++ b/dexlib2/src/main/java/org/jf/dexlib2/writer/DexWriter.java
@@ -236,7 +236,7 @@ public abstract class DexWriter<
         }
 
         byte[] buffer = new byte[4 * 1024];
-        InputStream input = dataStore.readAt(HeaderItem.HEADER_SIZE_OFFSET);
+        InputStream input = dataStore.readAt(HeaderItem.SIGNATURE_DATA_START_OFFSET);
         int bytesRead = input.read(buffer);
         while (bytesRead >= 0) {
             md.update(buffer, 0, bytesRead);
@@ -258,7 +258,7 @@ public abstract class DexWriter<
         Adler32 a32 = new Adler32();
 
         byte[] buffer = new byte[4 * 1024];
-        InputStream input = dataStore.readAt(HeaderItem.SIGNATURE_OFFSET);
+        InputStream input = dataStore.readAt(HeaderItem.CHECKSUM_DATA_START_OFFSET);
         int bytesRead = input.read(buffer);
         while (bytesRead >= 0) {
             a32.update(buffer, 0, bytesRead);