diff --git a/src/accountant.rs b/src/accountant.rs
index a531ff005e..b993965697 100644
--- a/src/accountant.rs
+++ b/src/accountant.rs
@@ -21,8 +21,8 @@ pub enum AccountingError {
 pub type Result<T> = result::Result<T, AccountingError>;
 
 pub struct Accountant {
-    pub historian: Historian<u64>,
-    pub balances: HashMap<PublicKey, u64>,
+    pub historian: Historian<i64>,
+    pub balances: HashMap<PublicKey, i64>,
     pub first_id: Sha256Hash,
     pub last_id: Sha256Hash,
 }
@@ -30,7 +30,7 @@ pub struct Accountant {
 impl Accountant {
     pub fn new_from_entries<I>(entries: I, ms_per_tick: Option<u64>) -> Self
     where
-        I: IntoIterator<Item = Entry<u64>>,
+        I: IntoIterator<Item = Entry<i64>>,
     {
         let mut entries = entries.into_iter();
 
@@ -39,7 +39,7 @@ impl Accountant {
         let entry0 = entries.next().unwrap();
         let start_hash = entry0.id;
 
-        let hist = Historian::<u64>::new(&start_hash, ms_per_tick);
+        let hist = Historian::<i64>::new(&start_hash, ms_per_tick);
         let mut acc = Accountant {
             historian: hist,
             balances: HashMap::new(),
@@ -74,7 +74,7 @@ impl Accountant {
         allow_deposits && from == to
     }
 
-    pub fn process_event(self: &mut Self, event: Event<u64>) -> Result<()> {
+    pub fn process_event(self: &mut Self, event: Event<i64>) -> Result<()> {
         if !verify_event(&event) {
             return Err(AccountingError::InvalidEvent);
         }
@@ -95,7 +95,7 @@ impl Accountant {
 
     fn process_verified_event(
         self: &mut Self,
-        event: &Event<u64>,
+        event: &Event<i64>,
         allow_deposits: bool,
     ) -> Result<()> {
         if !reserve_signature(&mut self.historian.signatures, event) {
@@ -122,7 +122,7 @@ impl Accountant {
 
     pub fn transfer(
         self: &mut Self,
-        n: u64,
+        n: i64,
         keypair: &Ed25519KeyPair,
         to: PublicKey,
     ) -> Result<Signature> {
@@ -139,7 +139,7 @@ impl Accountant {
         self.process_event(event).map(|_| sig)
     }
 
-    pub fn get_balance(self: &Self, pubkey: &PublicKey) -> Option<u64> {
+    pub fn get_balance(self: &Self, pubkey: &PublicKey) -> Option<i64> {
         self.balances.get(pubkey).map(|x| *x)
     }
 }
diff --git a/src/accountant_skel.rs b/src/accountant_skel.rs
index 4666e97edf..069b5cd851 100644
--- a/src/accountant_skel.rs
+++ b/src/accountant_skel.rs
@@ -14,7 +14,7 @@ pub enum Request {
     Transfer {
         from: PublicKey,
         to: PublicKey,
-        val: u64,
+        val: i64,
         last_id: Sha256Hash,
         sig: Signature,
     },
@@ -31,8 +31,8 @@ pub enum Request {
 
 #[derive(Serialize, Deserialize, Debug)]
 pub enum Response {
-    Balance { key: PublicKey, val: Option<u64> },
-    Entries { entries: Vec<Entry<u64>> },
+    Balance { key: PublicKey, val: Option<i64> },
+    Entries { entries: Vec<Entry<i64>> },
     Id { id: Sha256Hash, is_last: bool },
 }
 
diff --git a/src/accountant_stub.rs b/src/accountant_stub.rs
index 8016620a97..8e62addd36 100644
--- a/src/accountant_stub.rs
+++ b/src/accountant_stub.rs
@@ -29,7 +29,7 @@ impl AccountantStub {
         &self,
         from: PublicKey,
         to: PublicKey,
-        val: u64,
+        val: i64,
         last_id: Sha256Hash,
         sig: Signature,
     ) -> io::Result<usize> {
@@ -46,7 +46,7 @@ impl AccountantStub {
 
     pub fn transfer(
         &self,
-        n: u64,
+        n: i64,
         keypair: &Ed25519KeyPair,
         to: PublicKey,
         last_id: &Sha256Hash,
@@ -57,7 +57,7 @@ impl AccountantStub {
             .map(|_| sig)
     }
 
-    pub fn get_balance(&self, pubkey: &PublicKey) -> io::Result<Option<u64>> {
+    pub fn get_balance(&self, pubkey: &PublicKey) -> io::Result<Option<i64>> {
         let req = Request::GetBalance { key: *pubkey };
         let data = serialize(&req).expect("serialize GetBalance");
         self.socket.send_to(&data, &self.addr)?;
diff --git a/src/bin/genesis-block.rs b/src/bin/genesis-block.rs
index ce3e8e5898..dc620ff2e1 100644
--- a/src/bin/genesis-block.rs
+++ b/src/bin/genesis-block.rs
@@ -5,13 +5,13 @@ extern crate serde_json;
 extern crate silk;
 
 use silk::genesis::Genesis;
-use silk::log::verify_slice_u64;
+use silk::log::verify_slice_i64;
 use std::io::stdin;
 
 fn main() {
     let gen: Genesis = serde_json::from_reader(stdin()).unwrap();
     let entries = gen.create_entries();
-    verify_slice_u64(&entries, &entries[0].id);
+    verify_slice_i64(&entries, &entries[0].id);
     for x in entries {
         println!("{}", serde_json::to_string(&x).unwrap());
     }
diff --git a/src/genesis.rs b/src/genesis.rs
index df331532d2..a30f35883a 100644
--- a/src/genesis.rs
+++ b/src/genesis.rs
@@ -9,11 +9,11 @@ use untrusted::Input;
 #[derive(Serialize, Deserialize, Debug)]
 pub struct Creator {
     pub pubkey: PublicKey,
-    pub tokens: u64,
+    pub tokens: i64,
 }
 
 impl Creator {
-    pub fn new(tokens: u64) -> Self {
+    pub fn new(tokens: i64) -> Self {
         Creator {
             pubkey: get_pubkey(&generate_keypair()),
             tokens,
@@ -24,12 +24,12 @@ impl Creator {
 #[derive(Serialize, Deserialize, Debug)]
 pub struct Genesis {
     pub pkcs8: Vec<u8>,
-    pub tokens: u64,
+    pub tokens: i64,
     pub creators: Vec<Creator>,
 }
 
 impl Genesis {
-    pub fn new(tokens: u64, creators: Vec<Creator>) -> Self {
+    pub fn new(tokens: i64, creators: Vec<Creator>) -> Self {
         let rnd = SystemRandom::new();
         let pkcs8 = Ed25519KeyPair::generate_pkcs8(&rnd).unwrap().to_vec();
         println!("{:?}", pkcs8);
@@ -52,7 +52,7 @@ impl Genesis {
         get_pubkey(&self.get_keypair())
     }
 
-    pub fn create_transaction(&self, data: u64, to: &PublicKey) -> Event<u64> {
+    pub fn create_transaction(&self, data: i64, to: &PublicKey) -> Event<i64> {
         let last_id = self.get_seed();
         let from = self.get_pubkey();
         let sig = sign_transaction_data(&data, &self.get_keypair(), to, &last_id);
@@ -65,7 +65,7 @@ impl Genesis {
         }
     }
 
-    pub fn create_events(&self) -> Vec<Event<u64>> {
+    pub fn create_events(&self) -> Vec<Event<i64>> {
         let pubkey = self.get_pubkey();
         let event0 = Event::Tick;
         let event1 = self.create_transaction(self.tokens, &pubkey);
@@ -79,7 +79,7 @@ impl Genesis {
         events
     }
 
-    pub fn create_entries(&self) -> Vec<Entry<u64>> {
+    pub fn create_entries(&self) -> Vec<Entry<i64>> {
         create_entries(&self.get_seed(), self.create_events())
     }
 }
@@ -87,7 +87,7 @@ impl Genesis {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use log::verify_slice_u64;
+    use log::verify_slice_i64;
 
     #[test]
     fn test_create_events() {
@@ -114,12 +114,12 @@ mod tests {
     #[test]
     fn test_verify_entries() {
         let entries = Genesis::new(100, vec![]).create_entries();
-        assert!(verify_slice_u64(&entries, &entries[0].id));
+        assert!(verify_slice_i64(&entries, &entries[0].id));
     }
 
     #[test]
     fn test_verify_entries_with_transactions() {
         let entries = Genesis::new(100, vec![Creator::new(42)]).create_entries();
-        assert!(verify_slice_u64(&entries, &entries[0].id));
+        assert!(verify_slice_i64(&entries, &entries[0].id));
     }
 }
diff --git a/src/log.rs b/src/log.rs
index 3a254fd159..8d133b5b3c 100644
--- a/src/log.rs
+++ b/src/log.rs
@@ -130,7 +130,7 @@ pub fn verify_slice(events: &[Entry<Sha256Hash>], start_hash: &Sha256Hash) -> bo
 }
 
 /// Verifies the hashes and counts of a slice of events are all consistent.
-pub fn verify_slice_u64(events: &[Entry<u64>], start_hash: &Sha256Hash) -> bool {
+pub fn verify_slice_i64(events: &[Entry<i64>], start_hash: &Sha256Hash) -> bool {
     let genesis = [Entry::new_tick(Default::default(), start_hash)];
     let event_pairs = genesis.par_iter().chain(events).zip(events);
     event_pairs.all(|(x0, x1)| verify_entry(&x1, &x0.id))