diff --git a/atom/browser/in_app_purchase.h b/atom/browser/in_app_purchase.h
index 902d70deacf..d4957e8c97f 100644
--- a/atom/browser/in_app_purchase.h
+++ b/atom/browser/in_app_purchase.h
@@ -2,8 +2,8 @@
 // Use of this source code is governed by the MIT license that can be
 // found in the LICENSE file.
 
-#ifndef ATOM_BROWSER_UI_IN_APP_PURCHASE_H_
-#define ATOM_BROWSER_UI_IN_APP_PURCHASE_H_
+#ifndef ATOM_BROWSER_IN_APP_PURCHASE_H_
+#define ATOM_BROWSER_IN_APP_PURCHASE_H_
 
 #include <string>
 
@@ -27,4 +27,4 @@ void PurchaseProduct(const std::string& productID,
 
 }  // namespace in_app_purchase
 
-#endif  // ATOM_BROWSER_UI_IN_APP_PURCHASE_H_
+#endif  // ATOM_BROWSER_IN_APP_PURCHASE_H_
diff --git a/atom/browser/in_app_purchase_mac.mm b/atom/browser/in_app_purchase_mac.mm
index 9e859e7faac..5f4c994a0bc 100644
--- a/atom/browser/in_app_purchase_mac.mm
+++ b/atom/browser/in_app_purchase_mac.mm
@@ -112,8 +112,10 @@
  * @param product - The product to purchase.
  */
 - (void)runCallback:(bool)isProductValid {
-  content::BrowserThread::PostTask(content::BrowserThread::UI, FROM_HERE,
-                                   base::Bind(callback_, isProductValid));
+  if (callback_) {
+    content::BrowserThread::PostTask(content::BrowserThread::UI, FROM_HERE,
+                                     base::Bind(callback_, isProductValid));
+  }
 }
 
 @end
diff --git a/atom/browser/in_app_purchase_observer.h b/atom/browser/in_app_purchase_observer.h
index 450ee286b34..4b9f1d7b984 100644
--- a/atom/browser/in_app_purchase_observer.h
+++ b/atom/browser/in_app_purchase_observer.h
@@ -2,8 +2,8 @@
 // Use of this source code is governed by the MIT license that can be
 // found in the LICENSE file.
 
-#ifndef ATOM_BROWSER_UI_IN_APP_PURCHASE_OBSERVER_H_
-#define ATOM_BROWSER_UI_IN_APP_PURCHASE_OBSERVER_H_
+#ifndef ATOM_BROWSER_IN_APP_PURCHASE_OBSERVER_H_
+#define ATOM_BROWSER_IN_APP_PURCHASE_OBSERVER_H_
 
 #include <string>
 
@@ -38,4 +38,4 @@ void AddTransactionObserver(const InAppTransactionCallback& callback);
 
 }  // namespace in_app_purchase
 
-#endif  // ATOM_BROWSER_UI_IN_APP_PURCHASE_OBSERVER_H_
+#endif  // ATOM_BROWSER_IN_APP_PURCHASE_OBSERVER_H_
diff --git a/lib/browser/api/in-app-purchase.js b/lib/browser/api/in-app-purchase.js
index a0585e80dd9..e88b210ea9c 100644
--- a/lib/browser/api/in-app-purchase.js
+++ b/lib/browser/api/in-app-purchase.js
@@ -6,32 +6,25 @@ const v8Util = process.atomBinding('v8_util')
 module.exports = {
 
   canMakePayments: function() {
-    return binding.canMakePayments();
+    return binding.canMakePayments()
   },
 
   getReceiptURL: function() {
-    return binding.getReceiptURL();
+    return binding.getReceiptURL()
   },
 
-  purchaseProduct: function(productID, quantity, callback) {
-
+  purchaseProduct: function(productID, quantity = 1, callback) {
     if (typeof productID !== 'string') {
       throw new TypeError('productID must be a string')
     }
-
-    if (typeof quantity !== 'number') {
+    if (typeof quantity === 'function') {
       quantity = 1
+      callback = quantity
     }
-
-    if (typeof callback !== 'function') {
-      callback = function() {};
-    }
-
     return binding.purchaseProduct(productID, quantity, callback)
   },
 
   addTransactionListener: function(callback) {
-
     if (typeof callback !== 'function') {
       throw new TypeError('callback must be a function')
     }