diff --git a/src/Account/TSAccountManager.h b/src/Account/TSAccountManager.h
index 63673a450..a9ca71119 100644
--- a/src/Account/TSAccountManager.h
+++ b/src/Account/TSAccountManager.h
@@ -1,9 +1,5 @@
 //
-//  TSAccountManagement.h
-//  TextSecureKit
-//
-//  Created by Frederic Jacobs on 27/10/14.
-//  Copyright (c) 2014 Open Whisper Systems. All rights reserved.
+//  Copyright (c) 2017 Open Whisper Systems. All rights reserved.
 //
 
 #import <Foundation/Foundation.h>
@@ -21,6 +17,8 @@ static NSString *const TSRegistrationErrorUserInfoHTTPStatus = @"TSHTTPStatus";
 
 #pragma mark - Initializers
 
+- (instancetype)init NS_UNAVAILABLE;
+
 - (instancetype)initWithNetworkManager:(TSNetworkManager *)networkManager
                         storageManager:(TSStorageManager *)storageManager;
 
diff --git a/src/Account/TSAccountManager.m b/src/Account/TSAccountManager.m
index 0fbc7d8b7..63125df58 100644
--- a/src/Account/TSAccountManager.m
+++ b/src/Account/TSAccountManager.m
@@ -35,6 +35,8 @@ NS_ASSUME_NONNULL_BEGIN
     _networkManager = networkManager;
     _storageManager = storageManager;
 
+    OWSSingletonAssert();
+
     return self;
 }
 
diff --git a/src/Account/TSPrivacyPreferences.h b/src/Account/TSPrivacyPreferences.h
index c334db853..47c9af719 100644
--- a/src/Account/TSPrivacyPreferences.h
+++ b/src/Account/TSPrivacyPreferences.h
@@ -1,5 +1,6 @@
-//  Created by Michael Kirk on 11/7/16.
-//  Copyright © 2016 Open Whisper Systems. All rights reserved.
+//
+//  Copyright (c) 2017 Open Whisper Systems. All rights reserved.
+//
 
 #import "TSYapDatabaseObject.h"
 
@@ -7,6 +8,8 @@ NS_ASSUME_NONNULL_BEGIN
 
 @interface TSPrivacyPreferences : TSYapDatabaseObject
 
+- (instancetype)init NS_UNAVAILABLE;
+
 + (instancetype)sharedInstance;
 
 @property BOOL shouldBlockOnIdentityChange;
diff --git a/src/Account/TSPrivacyPreferences.m b/src/Account/TSPrivacyPreferences.m
index 635e8097a..fe3aa7054 100644
--- a/src/Account/TSPrivacyPreferences.m
+++ b/src/Account/TSPrivacyPreferences.m
@@ -1,5 +1,6 @@
-//  Created by Michael Kirk on 11/7/16.
-//  Copyright © 2016 Open Whisper Systems. All rights reserved.
+//
+//  Copyright (c) 2017 Open Whisper Systems. All rights reserved.
+//
 
 #import "TSPrivacyPreferences.h"
 
@@ -37,6 +38,8 @@ NSString *const TSPrivacyPreferencesSingletonKey = @"TSPrivacyPreferences";
 
     _shouldBlockOnIdentityChange = shouldBlockOnIdentityChange;
 
+    OWSSingletonAssert();
+
     return self;
 }
 
diff --git a/src/Contacts/ContactsUpdater.m b/src/Contacts/ContactsUpdater.m
index c2c22ce7f..daae4123b 100644
--- a/src/Contacts/ContactsUpdater.m
+++ b/src/Contacts/ContactsUpdater.m
@@ -25,6 +25,19 @@ NS_ASSUME_NONNULL_BEGIN
     return sharedInstance;
 }
 
+
+- (instancetype)init
+{
+    self = [super init];
+    if (!self) {
+        return self;
+    }
+
+    OWSSingletonAssert();
+
+    return self;
+}
+
 - (nullable SignalRecipient *)synchronousLookup:(NSString *)identifier error:(NSError **)error
 {
     dispatch_semaphore_t sema = dispatch_semaphore_create(0);
diff --git a/src/Contacts/PhoneNumberUtil.m b/src/Contacts/PhoneNumberUtil.m
index 63783da23..a54921d64 100644
--- a/src/Contacts/PhoneNumberUtil.m
+++ b/src/Contacts/PhoneNumberUtil.m
@@ -23,6 +23,8 @@
 
     if (self) {
         _nbPhoneNumberUtil = [[NBPhoneNumberUtil alloc] init];
+
+        OWSSingletonAssert();
     }
 
     return self;
diff --git a/src/Messages/OWSMessageSender.h b/src/Messages/OWSMessageSender.h
index 76b0a4ba4..7d8c865bf 100644
--- a/src/Messages/OWSMessageSender.h
+++ b/src/Messages/OWSMessageSender.h
@@ -1,5 +1,6 @@
-//  Created by Michael Kirk on 10/7/16.
-//  Copyright © 2016 Open Whisper Systems. All rights reserved.
+//
+//  Copyright (c) 2017 Open Whisper Systems. All rights reserved.
+//
 
 NS_ASSUME_NONNULL_BEGIN
 
@@ -23,6 +24,8 @@ NS_SWIFT_NAME(MessageSender)
     ContactsUpdater *_contactsUpdater;
 }
 
+- (instancetype)init NS_UNAVAILABLE;
+
 - (instancetype)initWithNetworkManager:(TSNetworkManager *)networkManager
                         storageManager:(TSStorageManager *)storageManager
                        contactsManager:(id<ContactsManagerProtocol>)contactsManager
diff --git a/src/Messages/OWSMessageSender.m b/src/Messages/OWSMessageSender.m
index c1c168c73..136f59c9b 100644
--- a/src/Messages/OWSMessageSender.m
+++ b/src/Messages/OWSMessageSender.m
@@ -288,6 +288,8 @@ NSString *const OWSMessageSenderRateLimitedException = @"RateLimitedException";
     _dbConnection = storageManager.newDatabaseConnection;
     _disappearingMessagesJob = [[OWSDisappearingMessagesJob alloc] initWithStorageManager:storageManager];
 
+    OWSSingletonAssert();
+
     return self;
 }
 
diff --git a/src/Messages/TSBlockingManager.m b/src/Messages/TSBlockingManager.m
index 032c3dc96..c10357402 100644
--- a/src/Messages/TSBlockingManager.m
+++ b/src/Messages/TSBlockingManager.m
@@ -66,6 +66,8 @@ NSString *const kTSStorageManager_SyncedBlockedPhoneNumbersKey = @"kTSStorageMan
     _storageManager = storageManager;
     _messageSender = messageSender;
 
+    OWSSingletonAssert();
+
     return self;
 }
 
diff --git a/src/Messages/TSMessagesManager.m b/src/Messages/TSMessagesManager.m
index 2f660901e..4ea23fc6d 100644
--- a/src/Messages/TSMessagesManager.m
+++ b/src/Messages/TSMessagesManager.m
@@ -105,7 +105,9 @@ NS_ASSUME_NONNULL_BEGIN
     _disappearingMessagesJob = [[OWSDisappearingMessagesJob alloc] initWithStorageManager:storageManager];
     _incomingMessageFinder = [[OWSIncomingMessageFinder alloc] initWithDatabase:storageManager.database];
     _blockingManager = [TSBlockingManager sharedManager];
-    
+
+    OWSSingletonAssert();
+
     return self;
 }
 
diff --git a/src/Network/API/TSNetworkManager.h b/src/Network/API/TSNetworkManager.h
index 08da37b94..62f06e3d3 100644
--- a/src/Network/API/TSNetworkManager.h
+++ b/src/Network/API/TSNetworkManager.h
@@ -28,6 +28,8 @@ NS_ASSUME_NONNULL_BEGIN
 
 @interface TSNetworkManager : NSObject
 
+- (instancetype)init NS_UNAVAILABLE;
+
 + (id)sharedManager;
 
 - (void)makeRequest:(TSRequest *)request
diff --git a/src/Network/API/TSNetworkManager.m b/src/Network/API/TSNetworkManager.m
index b79bb609a..e5e5bbc85 100644
--- a/src/Network/API/TSNetworkManager.m
+++ b/src/Network/API/TSNetworkManager.m
@@ -43,6 +43,8 @@ typedef void (^failureBlock)(NSURLSessionDataTask *task, NSError *error);
 
     _signalService = signalService;
 
+    OWSSingletonAssert();
+
     return self;
 }
 
diff --git a/src/Network/WebSockets/TSSocketManager.h b/src/Network/WebSockets/TSSocketManager.h
index 9a6e81457..079eea6a2 100644
--- a/src/Network/WebSockets/TSSocketManager.h
+++ b/src/Network/WebSockets/TSSocketManager.h
@@ -1,9 +1,5 @@
 //
-//  TSSocketManager.h
-//  TextSecureiOS
-//
-//  Created by Frederic Jacobs on 17/05/14.
-//  Copyright (c) 2014 Open Whisper Systems. All rights reserved.
+//  Copyright (c) 2017 Open Whisper Systems. All rights reserved.
 //
 
 #import <Foundation/Foundation.h>
@@ -23,6 +19,8 @@ extern NSString *const SocketConnectingNotification;
 
 @interface TSSocketManager : NSObject <SRWebSocketDelegate>
 
+- (instancetype)init NS_UNAVAILABLE;
+
 + (void)becomeActiveFromForeground;
 + (void)becomeActiveFromBackgroundExpectMessage:(BOOL)expected;
 
diff --git a/src/Network/WebSockets/TSSocketManager.m b/src/Network/WebSockets/TSSocketManager.m
index 68404d339..83a2ad4a0 100644
--- a/src/Network/WebSockets/TSSocketManager.m
+++ b/src/Network/WebSockets/TSSocketManager.m
@@ -61,6 +61,8 @@ NSString *const SocketConnectingNotification = @"SocketConnectingNotification";
 
     [self addObserver:self forKeyPath:@"status" options:0 context:kSocketStatusObservationContext];
 
+    OWSSingletonAssert();
+
     return self;
 }
 
diff --git a/src/Storage/TSStorageManager.h b/src/Storage/TSStorageManager.h
index 08f41e367..a0c9be407 100644
--- a/src/Storage/TSStorageManager.h
+++ b/src/Storage/TSStorageManager.h
@@ -16,6 +16,8 @@ extern NSString *const TSUIDatabaseConnectionDidUpdateNotification;
 
 @interface TSStorageManager : NSObject
 
+- (instancetype)init NS_UNAVAILABLE;
+
 + (instancetype)sharedManager;
 
 /**
diff --git a/src/Storage/TSStorageManager.m b/src/Storage/TSStorageManager.m
index eaca489b8..ace86f0a2 100644
--- a/src/Storage/TSStorageManager.m
+++ b/src/Storage/TSStorageManager.m
@@ -129,6 +129,8 @@ static NSString *keychainDBPassAccount    = @"TSDatabasePass";
 
             [NSException raise:TSStorageManagerExceptionNameNoDatabase format:@"Failed to initialize database."];
         }
+
+        OWSSingletonAssert();
     }
 
     return self;
diff --git a/src/Util/Asserts.h b/src/Util/Asserts.h
index d0cfbc728..6ec08413e 100755
--- a/src/Util/Asserts.h
+++ b/src/Util/Asserts.h
@@ -35,3 +35,37 @@ NSCAssert(0, @"Assertion failed: %s", CONVERT_EXPR_TO_STRING(X)); \
 #endif
 
 #endif
+
+#pragma mark - Singleton Asserts
+
+// The "singleton asserts" can be used to ensure
+// that we only create a singleton once.
+//
+// The simplest way to use them is the OWSSingletonAssert() macro.
+// It is intended to be used inside the singleton's initializer.
+//
+// If, however, a singleton has multiple possible initializers,
+// you need to:
+//
+// 1. Use OWSSingletonAssertFlag() outside the class definition.
+// 2. Use OWSSingletonAssertInit() in each initializer.
+#ifdef DEBUG
+
+#define OWSSingletonAssertFlag() static BOOL _isSingletonCreated = NO;
+
+#define OWSSingletonAssertInit()                                                                                       \
+    @synchronized([self class])                                                                                        \
+    {                                                                                                                  \
+        OWSAssert(!_isSingletonCreated);                                                                               \
+        _isSingletonCreated = YES;                                                                                     \
+    }
+
+#define OWSSingletonAssert() OWSSingletonAssertFlag() OWSSingletonAssertInit()
+
+#else
+
+#define OWSSingletonAssertFlag()
+#define OWSSingletonAssertInit()
+#define OWSSingletonAssert()
+
+#endif