diff --git a/lib/services/address/index.js b/lib/services/address/index.js
index 97144cd8..4da9f46d 100644
--- a/lib/services/address/index.js
+++ b/lib/services/address/index.js
@@ -60,7 +60,7 @@ AddressService.prototype.getAddressHistory = function(addresses, options, callba
     addresses = [addresses];
   }
 
-  async.mapLimit(addresses, 4, function(address, next) {
+  async.mapSeries(addresses, function(address, next) {
 
     self._getAddressHistory(address, options, next);
 
@@ -451,7 +451,7 @@ AddressService.prototype._getAddressHistory = function(address, options, callbac
       if (mempoolTxs.length <= 0) {
         return next();
       }
-      async.mapLimit(mempoolTxs, 4, function(tx, next) {
+      async.mapSeries(mempoolTxs, 4, function(tx, next) {
         self._transaction.setTxMetaInfo(tx, options, next);
       }, function(err, txs) {
         if (err) {
diff --git a/lib/services/mempool/index.js b/lib/services/mempool/index.js
index 61207ae2..ff3673ec 100644
--- a/lib/services/mempool/index.js
+++ b/lib/services/mempool/index.js
@@ -226,7 +226,7 @@ MempoolService.prototype._onTransaction = function(tx) {
       value: self._encoding.encodeMempoolTransactionValue(tx)
   }];
 
-  ops.concat(self._getAddressOperations(tx, true));
+  ops = ops.concat(self._getAddressOperations(tx, true));
   self._db.batch(ops, function(err) {
     if(err) {
       log.error(err);