diff --git a/atom.gyp b/atom.gyp
index 19eef43c06a6..cce3b2de432f 100644
--- a/atom.gyp
+++ b/atom.gyp
@@ -119,8 +119,6 @@
       'browser/ui/cocoa/atom_menu_controller.mm',
       'browser/ui/cocoa/event_processing_window.h',
       'browser/ui/cocoa/event_processing_window.mm',
-      'browser/ui/cocoa/nsalert_synchronous_sheet.h',
-      'browser/ui/cocoa/nsalert_synchronous_sheet.mm',
       'browser/ui/file_dialog.h',
       'browser/ui/file_dialog_gtk.cc',
       'browser/ui/file_dialog_mac.mm',
diff --git a/browser/ui/cocoa/nsalert_synchronous_sheet.h b/browser/ui/cocoa/nsalert_synchronous_sheet.h
deleted file mode 100644
index 5690bbb611d8..000000000000
--- a/browser/ui/cocoa/nsalert_synchronous_sheet.h
+++ /dev/null
@@ -1,10 +0,0 @@
-// Copyright (c) 2013 GitHub, Inc. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#import <Cocoa/Cocoa.h>
-
-@interface NSAlert (SynchronousSheet)
--(NSInteger) runModalSheetForWindow:(NSWindow*)aWindow;
--(NSInteger) runModalSheet;
-@end
diff --git a/browser/ui/cocoa/nsalert_synchronous_sheet.mm b/browser/ui/cocoa/nsalert_synchronous_sheet.mm
deleted file mode 100644
index a64652512687..000000000000
--- a/browser/ui/cocoa/nsalert_synchronous_sheet.mm
+++ /dev/null
@@ -1,51 +0,0 @@
-// Copyright (c) 2013 GitHub, Inc. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#import "browser/ui/cocoa/nsalert_synchronous_sheet.h"
-
-// Private methods -- use prefixes to avoid collisions with Apple's methods
-@interface NSAlert (SynchronousSheetPrivate)
--(IBAction) BE_stopSynchronousSheet:(id)sender;   // hide sheet & stop modal
--(void) BE_beginSheetModalForWindow:(NSWindow *)aWindow;
-@end
-
-@implementation NSAlert (SynchronousSheet)
-
--(NSInteger) runModalSheetForWindow:(NSWindow *)aWindow {
-  // Set ourselves as the target for button clicks
-  for (NSButton *button in [self buttons]) {
-    [button setTarget:self];
-    [button setAction:@selector(BE_stopSynchronousSheet:)];
-  }
-
-  // Bring up the sheet and wait until stopSynchronousSheet is triggered by a button click
-  [self performSelectorOnMainThread:@selector(BE_beginSheetModalForWindow:) withObject:aWindow waitUntilDone:YES];
-  NSInteger modalCode = [NSApp runModalForWindow:[self window]];
-
-  // This is called only after stopSynchronousSheet is called (that is,
-  // one of the buttons is clicked)
-  [NSApp performSelectorOnMainThread:@selector(endSheet:) withObject:[self window] waitUntilDone:YES];
-
-  // Remove the sheet from the screen
-  [[self window] performSelectorOnMainThread:@selector(orderOut:) withObject:self waitUntilDone:YES];
-
-  return modalCode;
-}
-
--(NSInteger) runModalSheet {
-  return [self runModalSheetForWindow:[NSApp mainWindow]];
-}
-
-
-#pragma mark Private methods
-
--(IBAction) BE_stopSynchronousSheet:(id)sender {
-  [NSApp stopModalWithCode:[sender  tag]];
-}
-
--(void) BE_beginSheetModalForWindow:(NSWindow *)aWindow {
-  [self beginSheetModalForWindow:aWindow modalDelegate:nil didEndSelector:nil contextInfo:nil];
-}
-
-@end
diff --git a/browser/ui/message_box_mac.mm b/browser/ui/message_box_mac.mm
index c6cbed42a855..5847d26195ab 100644
--- a/browser/ui/message_box_mac.mm
+++ b/browser/ui/message_box_mac.mm
@@ -9,24 +9,27 @@
 #include "base/callback.h"
 #include "base/strings/sys_string_conversions.h"
 #include "browser/native_window.h"
-#include "browser/ui/cocoa/nsalert_synchronous_sheet.h"
 
 @interface ModalDelegate : NSObject {
  @private
   atom::MessageBoxCallback callback_;
   NSAlert* alert_;
+  bool callEndModal_;
 }
 - (id)initWithCallback:(const atom::MessageBoxCallback&)callback
-              andAlert:(NSAlert*)alert;
+              andAlert:(NSAlert*)alert
+          callEndModal:(bool)flag;
 @end
 
 @implementation ModalDelegate
 
 - (id)initWithCallback:(const atom::MessageBoxCallback&)callback
-              andAlert:(NSAlert*)alert {
+              andAlert:(NSAlert*)alert
+          callEndModal:(bool)flag {
   if ((self = [super init])) {
     callback_ = callback;
     alert_ = alert;
+    callEndModal_ = flag;
   }
   return self;
 }
@@ -37,6 +40,9 @@
   callback_.Run(returnCode);
   [alert_ release];
   [self release];
+
+  if (callEndModal_)
+    [NSApp stopModal];
 }
 
 @end
@@ -76,6 +82,10 @@ NSAlert* CreateNSAlert(NativeWindow* parent_window,
   return alert;
 }
 
+void SetReturnCode(int* ret_code, int result) {
+  *ret_code = result;
+}
+
 }  // namespace
 
 int ShowMessageBox(NativeWindow* parent_window,
@@ -86,12 +96,26 @@ int ShowMessageBox(NativeWindow* parent_window,
                    const std::string& detail) {
   NSAlert* alert = CreateNSAlert(
       parent_window, type, buttons, title, message, detail);
-  [alert autorelease];
 
-  if (parent_window)
-    return [alert runModalSheetForWindow:parent_window->GetNativeWindow()];
-  else
-    return [alert runModal];
+  // Use runModal for synchronous alert without parent, since we don't have a
+  // window to wait for.
+  if (!parent_window)
+    return [[alert autorelease] runModal];
+
+  int ret_code = -1;
+  ModalDelegate* delegate = [[ModalDelegate alloc]
+      initWithCallback:base::Bind(&SetReturnCode, &ret_code)
+              andAlert:alert
+          callEndModal:true];
+
+  NSWindow* window = parent_window->GetNativeWindow();
+  [alert beginSheetModalForWindow:window
+                    modalDelegate:delegate
+                   didEndSelector:@selector(alertDidEnd:returnCode:contextInfo:)
+                      contextInfo:nil];
+
+  [NSApp runModalForWindow:window];
+  return ret_code;
 }
 
 void ShowMessageBox(NativeWindow* parent_window,
@@ -104,7 +128,8 @@ void ShowMessageBox(NativeWindow* parent_window,
   NSAlert* alert = CreateNSAlert(
       parent_window, type, buttons, title, message, detail);
   ModalDelegate* delegate = [[ModalDelegate alloc] initWithCallback:callback
-                                                           andAlert:alert];
+                                                           andAlert:alert
+                                                       callEndModal:false];
 
   NSWindow* window = parent_window ? parent_window->GetNativeWindow() : nil;
   [alert beginSheetModalForWindow:window