diff --git a/lib/services/address/history.js b/lib/services/address/history.js
index c20bc964..c5e91c5a 100644
--- a/lib/services/address/history.js
+++ b/lib/services/address/history.js
@@ -147,8 +147,26 @@ AddressHistory.prototype.sortAndPaginateCombinedArray = function() {
 };
 
 AddressHistory.sortByHeight = function(a, b) {
-  // TODO consider timestamp for mempool transactions
-  return a.height < b.height;
+  if (a.height < 0 && b.height < 0) {
+    // Both are from the mempool, compare timestamps
+    if (a.timestamp === b.timestamp) {
+      return 0;
+    } else {
+      return a.timestamp < b.timestamp ? 1 : -1;
+    }
+  } else if (a.height < 0 && b.height > 0) {
+    // A is from the mempool and B is in a block
+    return -1;
+  } else if (a.height > 0 && b.height < 0) {
+    // A is in a block and B is in the mempool
+    return 1;
+  } else if (a.height === b.height) {
+    // The heights are equal
+    return 0;
+  } else {
+    // Otherwise compare heights
+    return a.height < b.height ? 1 : -1;
+  }
 };
 
 AddressHistory.prototype.getDetailedInfo = function(txInfo, next) {
diff --git a/lib/services/address/index.js b/lib/services/address/index.js
index e99a3dae..7d74adb0 100644
--- a/lib/services/address/index.js
+++ b/lib/services/address/index.js
@@ -732,7 +732,7 @@ AddressService.prototype.isSpent = function(output, queryMempool, callback) {
 };
 
 /**
- * This will give the history for many addresses limited by a range of dates (to limit
+ * This will give the history for many addresses limited by a range of block heights (to limit
  * the database lookup times) and/or paginated to limit the results length.
  * @param {Array} addresses - An array of addresses
  * @param {Object} options - The options to limit the query
diff --git a/test/services/address/history.unit.js b/test/services/address/history.unit.js
index 61925bfa..9c24e05a 100644
--- a/test/services/address/history.unit.js
+++ b/test/services/address/history.unit.js
@@ -221,19 +221,165 @@ describe('Address Service History', function() {
     it('will sort latest to oldest using height', function() {
       var transactionInfo = [
         {
-          height: 12
+          height: 276328
         },
         {
-          height: 14,
+          height: 273845,
         },
         {
-          height: 13
+          height: 555655
+        },
+        {
+          height: 325496
+        },
+        {
+          height: 329186
+        },
+        {
+          height: 534195
         }
       ];
       transactionInfo.sort(AddressHistory.sortByHeight);
-      transactionInfo[0].height.should.equal(14);
-      transactionInfo[1].height.should.equal(13);
-      transactionInfo[2].height.should.equal(12);
+      transactionInfo[0].height.should.equal(555655);
+      transactionInfo[1].height.should.equal(534195);
+      transactionInfo[2].height.should.equal(329186);
+      transactionInfo[3].height.should.equal(325496);
+      transactionInfo[4].height.should.equal(276328);
+      transactionInfo[5].height.should.equal(273845);
+    });
+    it('mempool and tip with time in the future', function() {
+      var transactionInfo = [
+        {
+          timestamp: 1442050425439,
+          height: 14,
+        },
+        {
+          timestamp: 1442050424328,
+          height: -1
+        },
+        {
+          timestamp: 1442050424429,
+          height: -1
+        },
+        {
+          timestamp: 1442050425439,
+          height: 15
+        }
+      ];
+      transactionInfo.sort(AddressHistory.sortByHeight);
+      transactionInfo[0].height.should.equal(-1);
+      transactionInfo[0].timestamp.should.equal(1442050424429);
+      transactionInfo[1].height.should.equal(-1);
+      transactionInfo[1].timestamp.should.equal(1442050424328);
+      transactionInfo[2].height.should.equal(15);
+      transactionInfo[3].height.should.equal(14);
+    });
+    it('tip with time in the future and mempool', function() {
+      var transactionInfo = [
+        {
+          timestamp: 1442050425439,
+          height: 14,
+        },
+        {
+          timestamp: 1442050424328,
+          height: -1
+        }
+      ];
+      transactionInfo.sort(AddressHistory.sortByHeight);
+      transactionInfo[0].height.should.equal(-1);
+      transactionInfo[1].height.should.equal(14);
+    });
+    it('many transactions in the mempool', function() {
+      var transactionInfo = [
+        {
+          timestamp: 1442259670462,
+          height: -1
+        },
+        {
+          timestamp: 1442259785114,
+          height: -1
+        },
+        {
+          timestamp: 1442259759896,
+          height: -1
+        },
+        {
+          timestamp: 1442259692601,
+          height: -1
+        },
+        {
+          timestamp: 1442259692601,
+          height: 100
+        },
+        {
+          timestamp: 1442259749463,
+          height: -1
+        },
+        {
+          timestamp: 1442259737719,
+          height: -1
+        },
+        {
+          timestamp: 1442259773138,
+          height: -1,
+        }
+      ];
+      transactionInfo.sort(AddressHistory.sortByHeight);
+      transactionInfo[0].timestamp.should.equal(1442259785114);
+      transactionInfo[1].timestamp.should.equal(1442259773138);
+      transactionInfo[2].timestamp.should.equal(1442259759896);
+      transactionInfo[3].timestamp.should.equal(1442259749463);
+      transactionInfo[4].timestamp.should.equal(1442259737719);
+      transactionInfo[5].timestamp.should.equal(1442259692601);
+      transactionInfo[6].timestamp.should.equal(1442259670462);
+      transactionInfo[7].height.should.equal(100);
+    });
+    it('mempool and mempool', function() {
+      var transactionInfo = [
+        {
+          timestamp: 1442050424328,
+          height: -1
+        },
+        {
+          timestamp: 1442050425439,
+          height: -1,
+        }
+      ];
+      transactionInfo.sort(AddressHistory.sortByHeight);
+      transactionInfo[0].timestamp.should.equal(1442050425439);
+      transactionInfo[1].timestamp.should.equal(1442050424328);
+    });
+    it('mempool and mempool with the same timestamp', function() {
+      var transactionInfo = [
+        {
+          timestamp: 1442050425439,
+          height: -1,
+          txid: '1',
+        },
+        {
+          timestamp: 1442050425439,
+          height: -1,
+          txid: '2'
+        }
+      ];
+      transactionInfo.sort(AddressHistory.sortByHeight);
+      transactionInfo[0].txid.should.equal('1');
+      transactionInfo[1].txid.should.equal('2');
+    });
+    it('matching block heights', function() {
+      var transactionInfo = [
+        {
+          height: 325496,
+          txid: '1',
+        },
+        {
+          height: 325496,
+          txid: '2'
+        }
+      ];
+      transactionInfo.sort(AddressHistory.sortByHeight);
+      transactionInfo[0].txid.should.equal('1');
+      transactionInfo[1].txid.should.equal('2');
     });
   });