diff --git a/src/ledger/address.rs b/src/ledger/address.rs
index 88dd05a..c198b24 100644
--- a/src/ledger/address.rs
+++ b/src/ledger/address.rs
@@ -119,12 +119,12 @@ mod tests {
     fn addresses() {
         let ledger = Ledger::new();
 
-        assert_eq!(ledger.credentials.take().len(), 0);
+        assert_eq!(ledger.credentials.lock().unwrap().take().len(), 0);
 
         let credential = Ledger::generate_credential();
         ledger.add_credential(credential.clone());
 
-        let credentials = ledger.credentials.take();
+        let credentials = ledger.credentials.lock().unwrap().take();
         assert_eq!(credentials.len(), 1);
 
         assert_eq!(credential, credentials.get(0).unwrap().to_owned());
diff --git a/src/ledger/macros.rs b/src/ledger/macros.rs
index 75fa954..e97465f 100644
--- a/src/ledger/macros.rs
+++ b/src/ledger/macros.rs
@@ -7,11 +7,11 @@
 macro_rules! add_item_to_vec {
     ($member:expr, $item:expr) => {
         // Update item list.
-        let mut items = $member.take();
+        let mut items = $member.lock().unwrap().take();
         items.push($item);
 
         // Commit new change.
-        $member.set(items);
+        $member.lock().unwrap().set(items);
     };
 }
 /// Removes given item from a `Vec` member, which is guarded by a `Cell`.
@@ -19,21 +19,21 @@ macro_rules! add_item_to_vec {
 macro_rules! remove_item_from_vec {
     ($member:expr, $item:expr) => {
         // Get item list.
-        let mut items = $member.take();
+        let mut items = $member.lock().unwrap().take();
 
         // Delete given item.
         items.retain(|&i| i != $item);
 
         // Commit new change.
-        $member.set(items);
+        $member.lock().unwrap().set(items);
     };
 }
 /// Returns items of a `Vec` member, which is guarded by a `Cell`.
 #[macro_export]
 macro_rules! return_vec_item {
     ($member:expr) => {
-        let items = $member.take();
-        $member.set(items.clone());
+        let items = $member.lock().unwrap().take();
+        $member.lock().unwrap().set(items.clone());
 
         return items;
     };
@@ -43,7 +43,7 @@ macro_rules! return_vec_item {
 #[macro_export]
 macro_rules! update_item {
     ($member:expr, $item:expr) => {
-        $member.set($item);
+        $member.lock().unwrap().set($item);
     };
 }
 
@@ -51,20 +51,23 @@ macro_rules! update_item {
 #[macro_export]
 macro_rules! get_item {
     ($member:expr, $assignee:ident) => {
-        let $assignee = $member.take();
-        $member.set($assignee.clone());
+        let $assignee = $member.lock().unwrap().take();
+        $member.lock().unwrap().set($assignee.clone());
     };
 }
 
 #[cfg(test)]
 mod tests {
-    use std::cell::Cell;
+    use std::{
+        cell::Cell,
+        sync::{Arc, Mutex},
+    };
 
     /// Temporary struct for macro testing.
     #[derive(Default)]
     struct Test {
-        pub vec_member_1: Cell<Vec<isize>>,
-        pub int_member_1: Cell<isize>,
+        pub vec_member_1: Arc<Mutex<Cell<Vec<isize>>>>,
+        pub int_member_1: Arc<Mutex<Cell<isize>>>,
     }
 
     #[test]
diff --git a/src/ledger/mod.rs b/src/ledger/mod.rs
index 838d00c..093816b 100644
--- a/src/ledger/mod.rs
+++ b/src/ledger/mod.rs
@@ -7,7 +7,10 @@
 
 use address::UserCredential;
 use bitcoin::{OutPoint, Transaction};
-use std::cell::Cell;
+use std::{
+    cell::Cell,
+    sync::{Arc, Mutex},
+};
 
 mod address;
 mod errors;
@@ -19,20 +22,20 @@ mod utxo;
 /// Mock Bitcoin ledger.
 pub struct Ledger {
     /// User's keys and address.
-    credentials: Cell<Vec<UserCredential>>,
+    credentials: Arc<Mutex<Cell<Vec<UserCredential>>>>,
     /// Happened transactions.
-    transactions: Cell<Vec<Transaction>>,
+    transactions: Arc<Mutex<Cell<Vec<Transaction>>>>,
     /// Unspent transaction outputs.
-    utxos: Cell<Vec<OutPoint>>,
+    utxos: Arc<Mutex<Cell<Vec<OutPoint>>>>,
 }
 
 impl Ledger {
     /// Creates a new empty ledger.
     pub fn new() -> Self {
         Self {
-            credentials: Cell::new(Vec::new()),
-            utxos: Cell::new(Vec::new()),
-            transactions: Cell::new(Vec::new()),
+            credentials: Arc::new(Mutex::new(Cell::new(Vec::new()))),
+            utxos: Arc::new(Mutex::new(Cell::new(Vec::new()))),
+            transactions: Arc::new(Mutex::new(Cell::new(Vec::new()))),
         }
     }
 }