diff --git a/OpenVPN Adapter/OpenVPNAdapter.mm b/OpenVPN Adapter/OpenVPNAdapter.mm
index 3b5d23a..58bdd17 100644
--- a/OpenVPN Adapter/OpenVPNAdapter.mm	
+++ b/OpenVPN Adapter/OpenVPNAdapter.mm	
@@ -47,7 +47,7 @@
 
 #pragma mark - OpenVPNClient Lifecycle
 
-- (OpenVPNProperties *)applyConfiguration:(OpenVPNConfiguration *)configuration error:(NSError * _Nullable __autoreleasing *)error {
+- (OpenVPNProperties *)applyConfiguration:(OpenVPNConfiguration *)configuration error:(NSError * __autoreleasing *)error {
     ClientAPI::EvalConfig eval = self.vpnClient->eval_config(configuration.config);
     
     if (eval.error) {
@@ -65,7 +65,7 @@
     return [[OpenVPNProperties alloc] initWithEvalConfig:eval];
 }
 
-- (BOOL)provideCredentials:(OpenVPNCredentials *)credentials error:(NSError * _Nullable __autoreleasing *)error {
+- (BOOL)provideCredentials:(OpenVPNCredentials *)credentials error:(NSError * __autoreleasing *)error {
     ClientAPI::Status status = self.vpnClient->provide_creds(credentials.credentials);
     
     if (status.error) {
diff --git a/OpenVPN Adapter/OpenVPNCertificate.h b/OpenVPN Adapter/OpenVPNCertificate.h
index fb1c7f1..57d2f9c 100644
--- a/OpenVPN Adapter/OpenVPNCertificate.h	
+++ b/OpenVPN Adapter/OpenVPNCertificate.h	
@@ -8,17 +8,18 @@
 
 #import <Foundation/Foundation.h>
 
+NS_ASSUME_NONNULL_BEGIN
+
 @interface OpenVPNCertificate : NSObject
 
-+ (nullable OpenVPNCertificate *)certificateWithPEM:(nonnull NSData *)pemData
-                                              error:(out NSError * _Nullable * _Nullable)error;
++ (nullable OpenVPNCertificate *)certificateWithPEM:(NSData *)pemData error:(NSError **)error;
++ (nullable OpenVPNCertificate *)certificateWithDER:(NSData *)derData error:(NSError **)error;
 
-+ (nullable OpenVPNCertificate *)certificateWithDER:(nonnull NSData *)derData
-                                              error:(out NSError * _Nullable * _Nullable)error;
+- (instancetype) init NS_UNAVAILABLE;
 
-- (nonnull instancetype) init NS_UNAVAILABLE;
-
-- (nullable NSData *)pemData:(out NSError * _Nullable * _Nullable)error;
-- (nullable NSData *)derData:(out NSError * _Nullable * _Nullable)error;
+- (nullable NSData *)pemData:(NSError **)error;
+- (nullable NSData *)derData:(NSError **)error;
 
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/OpenVPN Adapter/OpenVPNCertificate.m b/OpenVPN Adapter/OpenVPNCertificate.m
index 826792e..907843c 100644
--- a/OpenVPN Adapter/OpenVPNCertificate.m	
+++ b/OpenVPN Adapter/OpenVPNCertificate.m	
@@ -20,7 +20,7 @@
 
 @implementation OpenVPNCertificate
 
-+ (OpenVPNCertificate *)certificateWithPEM:(NSData *)pemData error:(out NSError **)error {
++ (OpenVPNCertificate *)certificateWithPEM:(NSData *)pemData error:(NSError * __autoreleasing *)error {
     OpenVPNCertificate *certificate = [OpenVPNCertificate new];
     
     NSString *pemString = [[NSString alloc] initWithData:pemData encoding:NSUTF8StringEncoding];
@@ -37,7 +37,7 @@
     return certificate;
 }
 
-+ (OpenVPNCertificate *)certificateWithDER:(NSData *)derData error:(out NSError **)error {
++ (OpenVPNCertificate *)certificateWithDER:(NSData *)derData error:(NSError * __autoreleasing *)error {
     OpenVPNCertificate *certificate = [OpenVPNCertificate new];
     
     int result = mbedtls_x509_crt_parse_der(certificate.crt, derData.bytes, derData.length);
@@ -61,7 +61,7 @@
     return self;
 }
 
-- (NSData *)pemData:(out NSError **)error {
+- (NSData *)pemData:(NSError * __autoreleasing *)error {
     NSString *header = @"-----BEGIN CERTIFICATE-----\n";
     NSString *footer = @"-----END CERTIFICATE-----\n";
     
@@ -87,7 +87,7 @@
     return pemData;
 }
 
-- (NSData *)derData:(out NSError **)error {
+- (NSData *)derData:(NSError * __autoreleasing *)error {
     if (self.crt->raw.p == NULL || self.crt->raw.len == 0) {
         if (error) {
             *error = [NSError ovpn_errorObjectForMbedTLSError:MBEDTLS_ERR_X509_BAD_INPUT_DATA
diff --git a/OpenVPN Adapter/OpenVPNPacketFlowBridge.mm b/OpenVPN Adapter/OpenVPNPacketFlowBridge.mm
index 4c0cc9b..5b64e26 100644
--- a/OpenVPN Adapter/OpenVPNPacketFlowBridge.mm	
+++ b/OpenVPN Adapter/OpenVPNPacketFlowBridge.mm	
@@ -41,7 +41,7 @@ static void SocketCallback(CFSocketRef socket, CFSocketCallBackType type, CFData
     [bridge writePackets:@[packet] toPacketFlow:bridge.packetFlow];
 }
 
-- (BOOL)configureSocketsWithError:(NSError **)error {
+- (BOOL)configureSocketsWithError:(NSError * __autoreleasing *)error {
     int sockets[2];
     if (socketpair(PF_LOCAL, SOCK_DGRAM, IPPROTO_IP, sockets) == -1) {
         if (error) {
@@ -90,7 +90,7 @@ static void SocketCallback(CFSocketRef socket, CFSocketCallBackType type, CFData
     return YES;
 }
 
-- (BOOL)configureOptionsForSocket:(CFSocketRef)socket error:(NSError **)error {
+- (BOOL)configureOptionsForSocket:(CFSocketRef)socket error:(NSError * __autoreleasing *)error {
     CFSocketNativeHandle socketHandle = CFSocketGetNative(socket);
     
     int buf_value = 65536;
diff --git a/OpenVPN Adapter/OpenVPNPrivateKey.h b/OpenVPN Adapter/OpenVPNPrivateKey.h
index 61f8727..57bc4db 100644
--- a/OpenVPN Adapter/OpenVPNPrivateKey.h	
+++ b/OpenVPN Adapter/OpenVPNPrivateKey.h	
@@ -10,22 +10,26 @@
 
 typedef NS_ENUM(NSInteger, OpenVPNKeyType);
 
+NS_ASSUME_NONNULL_BEGIN
+
 @interface OpenVPNPrivateKey : NSObject
 
-+ (nullable OpenVPNPrivateKey *)keyWithPEM:(nonnull NSData *)pemData
++ (nullable OpenVPNPrivateKey *)keyWithPEM:(NSData *)pemData
                                   password:(nullable NSString *)password
-                                     error:(out NSError * _Nullable * _Nullable)error;
+                                     error:(NSError **)error;
 
-+ (nullable OpenVPNPrivateKey *)keyWithDER:(nonnull NSData *)derData
++ (nullable OpenVPNPrivateKey *)keyWithDER:(NSData *)derData
                                   password:(nullable NSString *)password
-                                     error:(out NSError * _Nullable * _Nullable)error;
+                                     error:(NSError **)error;
 
-- (nonnull instancetype) init NS_UNAVAILABLE;
+- (instancetype) init NS_UNAVAILABLE;
 
 @property (nonatomic, readonly) NSInteger size;
 @property (nonatomic, readonly) OpenVPNKeyType type;
 
-- (nullable NSData *)pemData:(out NSError * _Nullable * _Nullable)error;
-- (nullable NSData *)derData:(out NSError * _Nullable * _Nullable)error;
+- (nullable NSData *)pemData:(NSError **)error;
+- (nullable NSData *)derData:(NSError **)error;
 
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/OpenVPN Adapter/OpenVPNPrivateKey.m b/OpenVPN Adapter/OpenVPNPrivateKey.m
index a941878..d85cd90 100644
--- a/OpenVPN Adapter/OpenVPNPrivateKey.m	
+++ b/OpenVPN Adapter/OpenVPNPrivateKey.m	
@@ -21,7 +21,7 @@
 
 @implementation OpenVPNPrivateKey
 
-+ (nullable OpenVPNPrivateKey *)keyWithPEM:(NSData *)pemData password:(NSString *)password error:(out NSError **)error {
++ (OpenVPNPrivateKey *)keyWithPEM:(NSData *)pemData password:(NSString *)password error:(NSError * __autoreleasing *)error {
     OpenVPNPrivateKey *key = [OpenVPNPrivateKey new];
     
     NSString *pemString = [[NSString alloc] initWithData:pemData encoding:NSUTF8StringEncoding];
@@ -43,7 +43,7 @@
     return key;
 }
 
-+ (nullable OpenVPNPrivateKey *)keyWithDER:(NSData *)derData password:(NSString *)password error:(out NSError **)error {
++ (OpenVPNPrivateKey *)keyWithDER:(NSData *)derData password:(NSString *)password error:(NSError * __autoreleasing *)error {
     OpenVPNPrivateKey *key = [OpenVPNPrivateKey new];
     
     size_t password_length = password != nil ? strlen(password.UTF8String) : 0;
@@ -78,7 +78,7 @@
     return (OpenVPNKeyType)mbedtls_pk_get_type(self.ctx);
 }
 
-- (NSData *)pemData:(out NSError **)error {
+- (NSData *)pemData:(NSError * __autoreleasing *)error {
     size_t buffer_length = mbedtls_pk_get_len(self.ctx) * 10;
     unsigned char *pem_buffer = malloc(buffer_length);
     
@@ -99,7 +99,7 @@
     return pemData;
 }
 
-- (NSData *)derData:(out NSError **)error {
+- (NSData *)derData:(NSError * __autoreleasing *)error {
     size_t buffer_length = mbedtls_pk_get_len(self.ctx) * 10;
     unsigned char *der_buffer = malloc(buffer_length);