diff --git a/hintfile/Cargo.toml b/hintfile/Cargo.toml
index 0158f50..5f0f098 100644
--- a/hintfile/Cargo.toml
+++ b/hintfile/Cargo.toml
@@ -5,7 +5,7 @@ edition = "2021"
 
 [dependencies]
 bitcoin = { workspace = true }
-kernel = { package = "bitcoinkernel", git = "https://github.com/alexanderwiederin/rust-bitcoinkernel.git", rev = "31a53ebc81cf3648de2adea3ef7ee62b7a993221" }
+kernel = { package = "bitcoinkernel", git = "https://github.com/alexanderwiederin/rust-bitcoinkernel.git", rev = "b7b42d65a70f2c0e5fc8d1d024549bf857211046" }
 
 [[bin]]
 name = "construct"
diff --git a/hintfile/src/bin/construct.rs b/hintfile/src/bin/construct.rs
index ab02e5d..4205026 100644
--- a/hintfile/src/bin/construct.rs
+++ b/hintfile/src/bin/construct.rs
@@ -1,6 +1,5 @@
 use std::{fs::File, io::Write, sync::Arc};
 
-use bitcoin::{consensus, OutPoint};
 use hintfile::write_compact_size;
 use kernel::{ChainType, ChainstateManager, ChainstateManagerOptions, ContextBuilder, KernelError};
 
@@ -21,35 +20,32 @@ fn main() {
     let _context = Arc::new(ctx);
     let chainman = ChainstateManager::new(options).unwrap();
     println!("Chain state initialized");
-    let genesis = chainman.block_index_genesis();
+    // Writing the chain tip allows the client to know where to stop
     let tip = chainman.block_index_tip().block_hash().hash;
-    file.write_all(&tip).unwrap();
+    file.write_all(&tip).expect("file cannot be written to");
+
+    let genesis = chainman.block_index_genesis();
     let mut current = chainman.next_block_index(genesis).unwrap();
     loop {
         let block = chainman.read_block_data(&current).unwrap();
-        let bytes: Vec<u8> = block.into();
-        let block = consensus::deserialize::<bitcoin::Block>(&bytes).unwrap();
-        let (_, transactions) = block.into_parts();
-        println!("On block {}", current.height());
-        let mut delta: u64 = 0;
-        let mut block_offsets: Vec<u64> = Vec::new();
-        for tx in transactions {
-            let txid = tx.compute_txid();
-            for (index, _txout) in tx.outputs.iter().enumerate() {
-                let _outpoint = OutPoint {
-                    txid,
-                    vout: index as u32,
-                };
-                // if true
-                block_offsets.push(delta);
-                delta = 0;
+        println!("Block {} ...", current.height());
+        let mut block_unspents = Vec::new();
+        let mut curr = 0;
+        for i in 0..block.transaction_count() {
+            let transaction = block.transaction(i).unwrap();
+            for vout in 0..transaction.output_count() {
+                if chainman.have_coin(&transaction, vout) {
+                    println!("Found coin at offset {curr}");
+                    block_unspents.push(curr);
+                }
+                curr += 1;
             }
         }
+
         // Overflows 32 bit machines
-        let len_encode = block_offsets.len() as u64;
-        println!("Writing block offsets");
+        let len_encode = block_unspents.len() as u64;
         write_compact_size(len_encode, &mut file).expect("unexpected EOF");
-        for offset in block_offsets {
+        for offset in block_unspents {
             write_compact_size(offset, &mut file).expect("unexpected EOF");
         }
         match chainman.next_block_index(current) {
diff --git a/hintfile/src/lib.rs b/hintfile/src/lib.rs
index 6015460..efb65d1 100644
--- a/hintfile/src/lib.rs
+++ b/hintfile/src/lib.rs
@@ -3,7 +3,7 @@ use std::{
     io::{self, Read, Write},
 };
 
-use bitcoin::{BlockHeight, BlockHeightInterval};
+use bitcoin::{consensus, BlockHash, BlockHeight, BlockHeightInterval};
 
 pub fn write_compact_size<W: Write>(value: u64, writer: &mut W) -> Result<(), io::Error> {
     match value {
@@ -45,6 +45,7 @@ pub fn read_compact_size<R: Read>(reader: &mut R) -> Result<u64, io::Error> {
 #[derive(Debug)]
 pub struct Hints {
     map: BTreeMap<BlockHeight, Vec<u64>>,
+    assume_valid: BlockHash,
 }
 
 impl Hints {
@@ -54,6 +55,9 @@ impl Hints {
     pub fn from_file<R: Read>(reader: &mut R) -> Self {
         let mut map = BTreeMap::new();
         let mut height = BlockHeight::from_u32(1);
+        let mut buf = [0; 32];
+        reader.read_exact(&mut buf).expect("empty file");
+        let assume_valid = consensus::deserialize::<BlockHash>(&buf).expect("empty file.");
         while let Ok(count) = read_compact_size(reader) {
             // panics on 32 bit machines
             let mut offsets = Vec::with_capacity(count as usize);
@@ -65,7 +69,12 @@ impl Hints {
                 .checked_add(BlockHeightInterval::from_u32(1))
                 .expect("hintfile absurdly large.")
         }
-        Self { map }
+        Self { map, assume_valid }
+    }
+
+    /// Get the last hash encoded in the hintfile.
+    pub fn stop_hash(&self) -> BlockHash {
+        self.assume_valid
     }
 
     /// # Panics