diff --git a/class/User.js b/class/User.js
index 51c730d..d4b6060 100644
--- a/class/User.js
+++ b/class/User.js
@@ -294,8 +294,8 @@ export class User {
    * @returns {Promise<void>}
    */
   async accountForPosibleTxids() {
-    let imported_txids = await this._redis.lrange('imported_txids_for_' + this._userid, 0, -1);
     let onchain_txs = await this.getTxs();
+    let imported_txids = await this._redis.lrange('imported_txids_for_' + this._userid, 0, -1);
     for (let tx of onchain_txs) {
       if (tx.type !== 'bitcoind_tx') continue;
       let already_imported = false;
@@ -304,6 +304,16 @@ export class User {
       }
 
       if (!already_imported && tx.category === 'receive') {
+        let locked = await this._redis.get('importing_' + tx.txid);
+        if (locked) {
+          // race condition, someone's already importing this tx
+          return;
+        }
+
+        // locking...
+        await this._redis.set('importing_' + tx.txid, 1);
+        await this._redis.expire('importing_' + tx.txid, 3600);
+
         let userBalance = await this.getBalance();
         userBalance += new BigNumber(tx.amount).multipliedBy(100000000).toNumber();
         await this.saveBalance(userBalance);
diff --git a/doc/schema.md b/doc/schema.md
index c115e58..7c645d1 100644
--- a/doc/schema.md
+++ b/doc/schema.md
@@ -9,6 +9,7 @@ User storage schema
 * access_token_for_{userid} = {access_token}
 * userid_for_{refresh_token} = {userid}
 * refresh_token_for_{userid} = {access_token}
+* importing_{txid} = 1 `atomic lock when processing topup tx`