diff --git a/lib/order/market.js b/lib/order/market.js
index c84dc39..e82734f 100644
--- a/lib/order/market.js
+++ b/lib/order/market.js
@@ -4,7 +4,7 @@ var _ = require('lodash');
 
 module.exports = function (action, quantity, transmitOrder, goodAfterTime, goodTillDate) {
   assert(_.isString(action), 'Action must be a string.');
-  assert(_.isNumber(quantity), 'Quantity must be a string.');
+  assert(_.isNumber(quantity), 'Quantity must be a number.');
 
   if (transmitOrder === undefined) {
     transmitOrder = true;
diff --git a/lib/order/marketClose.js b/lib/order/marketClose.js
index 6e1ce88..4ce37dd 100644
--- a/lib/order/marketClose.js
+++ b/lib/order/marketClose.js
@@ -4,7 +4,7 @@ var _ = require('lodash');
 
 module.exports = function (action, quantity, transmitOrder) {
   assert(_.isString(action), 'Action must be a string.');
-  assert(_.isNumber(quantity), 'Quantity must be a string.');
+  assert(_.isNumber(quantity), 'Quantity must be a number.');
 
   if (transmitOrder === undefined) {
     transmitOrder = true;
diff --git a/lib/order/stopLimit.js b/lib/order/stopLimit.js
index 651512c..f9c2def 100644
--- a/lib/order/stopLimit.js
+++ b/lib/order/stopLimit.js
@@ -4,7 +4,7 @@ var _ = require('lodash');
 
 module.exports = function (action, quantity, limitPrice, stopPrice, transmitOrder, parentId, tif) {
   assert(_.isString(action), 'Action must be a string.');
-  assert(_.isNumber(quantity), 'Quantity must be a string.');
+  assert(_.isNumber(quantity), 'Quantity must be a number.');
   assert(_.isNumber(stopPrice), 'Stop price must be a number.');
   assert(_.isNumber(limitPrice), 'Limit price must be a number.');