Account.h

//
//  Account.h
//  Recurring
//
//  Created by Colby Ludwig on 2015-08-19.
//  Copyright (c) 2015 Colby Ludwig. All rights reserved.
//

#import <Realm/Realm.h>
@class Bill;

@interface Account : RLMObject

@property NSString *name;
@property RLMArray<Bill *><Bill> *bills;

@end

// This protocol enables typed collections. i.e.:
// RLMArray<Account>
RLM_ARRAY_TYPE(Account)

Bill.h

//
//  Bill.h
//  Recurring
//
//  Created by Colby Ludwig on 2015-08-19.
//  Copyright (c) 2015 Colby Ludwig. All rights reserved.
//

#import <Realm/Realm.h>
@class Account;

@interface Bill : RLMObject

@property NSString *name;
@property NSDecimalNumber *cost;

@property NSDate *startDate;
@property NSCalendarUnit repeatUnit;
@property NSInteger repeatInterval;

@property Account *fromAccount;

@property NSDate *notificationDate;

@end

// This protocol enables typed collections. i.e.:
// RLMArray<Bill>
RLM_ARRAY_TYPE(Bill)

The build fails on L15 of Account.h.