diff --git a/SignalServiceKit/src/Messages/OWSMessageSender.m b/SignalServiceKit/src/Messages/OWSMessageSender.m
index 0e26cc45e..1ac44d17a 100644
--- a/SignalServiceKit/src/Messages/OWSMessageSender.m
+++ b/SignalServiceKit/src/Messages/OWSMessageSender.m
@@ -1212,8 +1212,8 @@ NSString *const OWSMessageSenderRateLimitedException = @"RateLimitedException";
 {
     if (![storage containsSession:identifier deviceId:[deviceNumber intValue]]) {
         __block dispatch_semaphore_t sema = dispatch_semaphore_create(0);
-        __block PreKeyBundle *bundle;
-        __block NSException *exception;
+        __block PreKeyBundle *_Nullable bundle;
+        __block NSException *_Nullable exception;
         [self.networkManager makeRequest:[[TSRecipientPrekeyRequest alloc] initWithRecipient:identifier
                                                                                     deviceId:[deviceNumber stringValue]]
             success:^(NSURLSessionDataTask *task, id responseObject) {
diff --git a/SignalServiceKit/src/Messages/PreKeyBundle+jsonDict.h b/SignalServiceKit/src/Messages/PreKeyBundle+jsonDict.h
index 030166085..37729e50f 100644
--- a/SignalServiceKit/src/Messages/PreKeyBundle+jsonDict.h
+++ b/SignalServiceKit/src/Messages/PreKeyBundle+jsonDict.h
@@ -1,15 +1,15 @@
 //
-//  PreKeyBundle+jsonDict.h
-//  Signal
-//
-//  Created by Frederic Jacobs on 26/11/14.
-//  Copyright (c) 2014 Open Whisper Systems. All rights reserved.
+//  Copyright (c) 2017 Open Whisper Systems. All rights reserved.
 //
 
 #import "PreKeyBundle.h"
 
+NS_ASSUME_NONNULL_BEGIN
+
 @interface PreKeyBundle (jsonDict)
 
-+ (PreKeyBundle *)preKeyBundleFromDictionary:(NSDictionary *)dictionary forDeviceNumber:(NSNumber *)number;
++ (nullable PreKeyBundle *)preKeyBundleFromDictionary:(NSDictionary *)dictionary forDeviceNumber:(NSNumber *)number;
 
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/SignalServiceKit/src/Messages/PreKeyBundle+jsonDict.m b/SignalServiceKit/src/Messages/PreKeyBundle+jsonDict.m
index 8984c34e5..b6d6089ca 100644
--- a/SignalServiceKit/src/Messages/PreKeyBundle+jsonDict.m
+++ b/SignalServiceKit/src/Messages/PreKeyBundle+jsonDict.m
@@ -5,17 +5,27 @@
 #import "NSData+Base64.h"
 #import "PreKeyBundle+jsonDict.h"
 
+NS_ASSUME_NONNULL_BEGIN
+
 @implementation PreKeyBundle (jsonDict)
 
-+ (PreKeyBundle *)preKeyBundleFromDictionary:(NSDictionary *)dictionary forDeviceNumber:(NSNumber *)number {
++ (nullable PreKeyBundle *)preKeyBundleFromDictionary:(NSDictionary *)dictionary forDeviceNumber:(NSNumber *)number
+{
     PreKeyBundle *bundle        = nil;
-    NSString *identityKeyString = [dictionary objectForKey:@"identityKey"];
-    NSArray *devicesArray       = [dictionary objectForKey:@"devices"];
 
-    if (!(identityKeyString && [devicesArray isKindOfClass:[NSArray class]])) {
-        DDLogError(@"Failed to get identity key or messages array from server request");
+    id identityKeyObject = [dictionary objectForKey:@"identityKey"];
+    if (![identityKeyObject isKindOfClass:[NSString class]]) {
+        OWSFail(@"Unexpected identityKeyObject: %@", identityKeyObject);
+        return nil;
+    }
+    NSString *identityKeyString = (NSString *)identityKeyObject;
+
+    id devicesObject = [dictionary objectForKey:@"devices"];
+    if (![devicesObject isKindOfClass:[NSArray class]]) {
+        OWSFail(@"Unexpected devicesObject: %@", devicesObject);
         return nil;
     }
+    NSArray *devicesArray = (NSArray *)devicesObject;
 
     NSData *identityKey = [NSData dataFromBase64StringNoPadding:identityKeyString];
 
@@ -108,3 +118,5 @@
 }
 
 @end
+
+NS_ASSUME_NONNULL_END